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 $107.42   5.723%   $113.5676   $113.57   $113.55   $113.60  
  Purchase #2 $220.91   5.727%   $233.5615   $233.56   $233.55   $233.60  
  Purchase #3 $87.51   7.203%   $93.8133   $93.81   $93.80   $93.80  
  Purchase #4 $241.88   8.773%   $263.1001   $263.10   $263.10   $263.10  
  Purchase #5 $42.62   11.342%   $47.454   $47.45   $47.45   $47.50  
  Purchase #6 $58.87   10.843%   $65.2533   $65.25   $65.25   $65.30  
  Purchase #7 $160.64   6.355%   $170.8487   $170.85   $170.85   $170.80  
  7 purchase totals = $919.85       $987.5985   $987.59   $987.55   $987.70