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 $48.40   3.761%   $50.2203   $50.22   $50.20   $50.20  
  Purchase #2 $202.50   9.706%   $222.1547   $222.15   $222.15   $222.20  
  Purchase #3 $50.73   10.354%   $55.9826   $55.98   $56.00   $56.00  
  Purchase #4 $245.42   8.872%   $267.1937   $267.19   $267.20   $267.20  
  Purchase #5 $213.32   12.280%   $239.5157   $239.52   $239.50   $239.50  
  Purchase #6 $12.64   12.112%   $14.171   $14.17   $14.15   $14.20  
  Purchase #7 $169.53   10.513%   $187.3527   $187.35   $187.35   $187.40  
  7 purchase totals = $942.54       $1,036.5907   $1,036.58   $1,036.55   $1,036.70