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 $144.41   12.848%   $162.9638   $162.96   $162.95   $163.00  
  Purchase #2 $86.56   9.463%   $94.7512   $94.75   $94.75   $94.80  
  Purchase #3 $174.28   11.348%   $194.0573   $194.06   $194.05   $194.10  
  Purchase #4 $45.95   5.568%   $48.5085   $48.51   $48.50   $48.50  
  Purchase #5 $168.65   8.692%   $183.3091   $183.31   $183.30   $183.30  
  Purchase #6 $249.42   5.738%   $263.7317   $263.73   $263.75   $263.70  
  Purchase #7 $84.31   11.480%   $93.9888   $93.99   $94.00   $94.00  
  7 purchase totals = $953.58       $1,041.3104   $1,041.31   $1,041.30   $1,041.40