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 $8.94   4.421%   $9.3352   $9.34   $9.35   $9.30  
  Purchase #2 $154.72   6.348%   $164.5416   $164.54   $164.55   $164.50  
  Purchase #3 $164.72   10.618%   $182.21   $182.21   $182.20   $182.20  
  Purchase #4 $216.63   6.836%   $231.4388   $231.44   $231.45   $231.40  
  Purchase #5 $47.52   5.568%   $50.1659   $50.17   $50.15   $50.20  
  Purchase #6 $60.78   8.169%   $65.7451   $65.75   $65.75   $65.70  
  Purchase #7 $119.80   12.182%   $134.394   $134.39   $134.40   $134.40  
  7 purchase totals = $773.11       $837.8306   $837.84   $837.85   $837.70