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 $56.25   11.614%   $62.7829   $62.78   $62.80   $62.80  
  Purchase #2 $147.46   8.409%   $159.8599   $159.86   $159.85   $159.90  
  Purchase #3 $112.82   9.663%   $123.7218   $123.72   $123.70   $123.70  
  Purchase #4 $49.57   7.345%   $53.2109   $53.21   $53.20   $53.20  
  Purchase #5 $51.37   13.536%   $58.3234   $58.32   $58.30   $58.30  
  Purchase #6 $181.54   5.206%   $190.991   $190.99   $191.00   $191.00  
  Purchase #7 $97.40   11.184%   $108.2932   $108.29   $108.30   $108.30  
  7 purchase totals = $696.41       $757.1831   $757.17   $757.15   $757.20