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 $65.73   13.669%   $74.7146   $74.71   $74.70   $74.70  
  Purchase #2 $206.82   8.426%   $224.2467   $224.25   $224.25   $224.20  
  Purchase #3 $231.50   6.843%   $247.3415   $247.34   $247.35   $247.30  
  Purchase #4 $61.56   8.386%   $66.7224   $66.72   $66.70   $66.70  
  Purchase #5 $228.95   8.505%   $248.4222   $248.42   $248.40   $248.40  
  Purchase #6 $229.85   4.419%   $240.0071   $240.01   $240.00   $240.00  
  Purchase #7 $17.31   3.260%   $17.8743   $17.87   $17.85   $17.90  
  7 purchase totals = $1,041.72       $1,119.3288   $1,119.32   $1,119.25   $1,119.20