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 $45.33   3.192%   $46.7769   $46.78   $46.80   $46.80  
  Purchase #2 $206.93   9.635%   $226.8677   $226.87   $226.85   $226.90  
  Purchase #3 $85.80   12.510%   $96.5336   $96.53   $96.55   $96.50  
  Purchase #4 $211.72   6.732%   $225.973   $225.97   $225.95   $226.00  
  Purchase #5 $166.70   5.292%   $175.5218   $175.52   $175.50   $175.50  
  Purchase #6 $239.85   12.238%   $269.2028   $269.20   $269.20   $269.20  
  Purchase #7 $10.42   7.419%   $11.1931   $11.19   $11.20   $11.20  
  7 purchase totals = $966.75       $1,052.0689   $1,052.06   $1,052.05   $1,052.10