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 $61.47   11.867%   $68.7646   $68.76   $68.75   $68.80  
  Purchase #2 $127.90   12.358%   $143.7059   $143.71   $143.70   $143.70  
  Purchase #3 $164.29   3.138%   $169.4454   $169.45   $169.45   $169.40  
  Purchase #4 $229.38   6.833%   $245.0535   $245.05   $245.05   $245.10  
  Purchase #5 $61.62   5.297%   $64.884   $64.88   $64.90   $64.90  
  Purchase #6 $137.80   7.395%   $147.9903   $147.99   $148.00   $148.00  
  Purchase #7 $220.30   12.550%   $247.9477   $247.95   $247.95   $247.90  
  7 purchase totals = $1,002.76       $1,087.7914   $1,087.79   $1,087.80   $1,087.80