Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $229.86   12.702%   $259.0568   $259.06   $259.05   $259.10  
  Purchase #2 $146.49   7.127%   $156.9303   $156.93   $156.95   $156.90  
  Purchase #3 $243.99   10.384%   $269.3259   $269.33   $269.35   $269.30  
  Purchase #4 $226.66   13.780%   $257.8937   $257.89   $257.90   $257.90  
  Purchase #5 $97.59   9.584%   $106.943   $106.94   $106.95   $106.90  
  Purchase #6 $138.78   4.855%   $145.5178   $145.52   $145.50   $145.50  
  Purchase #7 $184.82   11.641%   $206.3349   $206.33   $206.35   $206.30  
  7 purchase totals = $1,268.19       $1,402.0024   $1,402.00   $1,402.05   $1,401.90