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 $56.49   11.332%   $62.8914   $62.89   $62.90   $62.90  
  Purchase #2 $85.48   3.761%   $88.6949   $88.69   $88.70   $88.70  
  Purchase #3 $126.99   9.645%   $139.2382   $139.24   $139.25   $139.20  
  Purchase #4 $173.36   4.142%   $180.5406   $180.54   $180.55   $180.50  
  Purchase #5 $165.36   4.358%   $172.5664   $172.57   $172.55   $172.60  
  Purchase #6 $161.53   12.424%   $181.5985   $181.60   $181.60   $181.60  
  Purchase #7 $102.99   3.847%   $106.952   $106.95   $106.95   $107.00  
  7 purchase totals = $872.20       $932.4820   $932.48   $932.50   $932.50