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 $54.72   12.862%   $61.7581   $61.76   $61.75   $61.80  
  Purchase #2 $172.95   3.796%   $179.5152   $179.52   $179.50   $179.50  
  Purchase #3 $183.27   4.419%   $191.3687   $191.37   $191.35   $191.40  
  Purchase #4 $61.96   4.842%   $64.9601   $64.96   $64.95   $65.00  
  Purchase #5 $218.25   13.107%   $246.856   $246.86   $246.85   $246.90  
  Purchase #6 $77.81   5.397%   $82.0094   $82.01   $82.00   $82.00  
  Purchase #7 $189.51   8.167%   $204.9873   $204.99   $205.00   $205.00  
  7 purchase totals = $958.47       $1,031.4548   $1,031.47   $1,031.40   $1,031.60