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 $52.58   4.756%   $55.0807   $55.08   $55.10   $55.10  
  Purchase #2 $174.33   13.419%   $197.7233   $197.72   $197.70   $197.70  
  Purchase #3 $250.36   3.803%   $259.8812   $259.88   $259.90   $259.90  
  Purchase #4 $111.33   10.232%   $122.7213   $122.72   $122.70   $122.70  
  Purchase #5 $41.33   13.722%   $47.0013   $47.00   $47.00   $47.00  
  Purchase #6 $47.71   13.634%   $54.2148   $54.21   $54.20   $54.20  
  Purchase #7 $240.43   7.529%   $258.532   $258.53   $258.55   $258.50  
  7 purchase totals = $918.07       $995.1546   $995.14   $995.15   $995.10