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 $113.29   10.742%   $125.4596   $125.46   $125.45   $125.50  
  Purchase #2 $116.83   9.499%   $127.9277   $127.93   $127.95   $127.90  
  Purchase #3 $15.74   4.193%   $16.4   $16.40   $16.40   $16.40  
  Purchase #4 $247.52   7.421%   $265.8885   $265.89   $265.90   $265.90  
  Purchase #5 $35.75   9.572%   $39.172   $39.17   $39.15   $39.20  
  Purchase #6 $211.81   7.798%   $228.3269   $228.33   $228.35   $228.30  
  Purchase #7 $135.91   6.686%   $144.9969   $145.00   $145.00   $145.00  
  7 purchase totals = $876.85       $948.1716   $948.18   $948.20   $948.20