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 $57.95   10.432%   $63.9953   $64.00   $64.00   $64.00  
  Purchase #2 $23.39   3.348%   $24.1731   $24.17   $24.15   $24.20  
  Purchase #3 $194.26   13.453%   $220.3938   $220.39   $220.40   $220.40  
  Purchase #4 $148.38   3.103%   $152.9842   $152.98   $153.00   $153.00  
  Purchase #5 $54.91   9.579%   $60.1698   $60.17   $60.15   $60.20  
  Purchase #6 $84.57   11.750%   $94.507   $94.51   $94.50   $94.50  
  Purchase #7 $135.56   3.592%   $140.4293   $140.43   $140.45   $140.40  
  7 purchase totals = $699.02       $756.6525   $756.65   $756.65   $756.70