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 $40.72   10.393%   $44.952   $44.95   $44.95   $45.00  
  Purchase #2 $63.93   11.860%   $71.5121   $71.51   $71.50   $71.50  
  Purchase #3 $24.34   8.444%   $26.3953   $26.40   $26.40   $26.40  
  Purchase #4 $233.34   4.755%   $244.4353   $244.44   $244.45   $244.40  
  Purchase #5 $107.45   9.491%   $117.6481   $117.65   $117.65   $117.60  
  Purchase #6 $110.37   11.323%   $122.8672   $122.87   $122.85   $122.90  
  Purchase #7 $216.29   12.407%   $243.1251   $243.13   $243.15   $243.10  
  7 purchase totals = $796.44       $870.9351   $870.95   $870.95   $870.90