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 $57.65   8.459%   $62.5266   $62.53   $62.55   $62.50  
  Purchase #2 $189.99   5.744%   $200.903   $200.90   $200.90   $200.90  
  Purchase #3 $149.79   13.632%   $170.2094   $170.21   $170.20   $170.20  
  Purchase #4 $147.54   12.270%   $165.6432   $165.64   $165.65   $165.60  
  Purchase #5 $34.64   3.258%   $35.7686   $35.77   $35.75   $35.80  
  Purchase #6 $121.82   10.127%   $134.1567   $134.16   $134.15   $134.20  
  Purchase #7 $116.39   7.691%   $125.3416   $125.34   $125.35   $125.30  
  7 purchase totals = $817.82       $894.5491   $894.55   $894.55   $894.50