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 $55.84   11.374%   $62.1912   $62.19   $62.20   $62.20  
  Purchase #2 $213.85   9.670%   $234.5293   $234.53   $234.55   $234.50  
  Purchase #3 $184.56   9.407%   $201.9216   $201.92   $201.90   $201.90  
  Purchase #4 $107.65   4.336%   $112.3177   $112.32   $112.30   $112.30  
  Purchase #5 $28.89   8.318%   $31.2931   $31.29   $31.30   $31.30  
  Purchase #6 $87.48   10.456%   $96.6269   $96.63   $96.65   $96.60  
  Purchase #7 $134.81   13.681%   $153.2534   $153.25   $153.25   $153.30  
  7 purchase totals = $813.08       $892.1332   $892.13   $892.15   $892.10