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 $79.58   11.157%   $88.4587   $88.46   $88.45   $88.50  
  Purchase #2 $149.66   10.581%   $165.4955   $165.50   $165.50   $165.50  
  Purchase #3 $152.81   7.768%   $164.6803   $164.68   $164.70   $164.70  
  Purchase #4 $76.42   7.654%   $82.2692   $82.27   $82.25   $82.30  
  Purchase #5 $58.66   3.217%   $60.5471   $60.55   $60.55   $60.50  
  Purchase #6 $217.62   7.757%   $234.5008   $234.50   $234.50   $234.50  
  Purchase #7 $133.31   11.764%   $148.9926   $148.99   $149.00   $149.00  
  7 purchase totals = $868.06       $944.9442   $944.95   $944.95   $945.00