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 $119.99   4.669%   $125.5923   $125.59   $125.60   $125.60  
  Purchase #2 $128.69   10.734%   $142.5036   $142.50   $142.50   $142.50  
  Purchase #3 $110.52   6.472%   $117.6729   $117.67   $117.65   $117.70  
  Purchase #4 $165.83   5.112%   $174.3072   $174.31   $174.30   $174.30  
  Purchase #5 $30.86   8.746%   $33.559   $33.56   $33.55   $33.60  
  Purchase #6 $206.49   12.338%   $231.9667   $231.97   $231.95   $232.00  
  Purchase #7 $102.76   12.774%   $115.8866   $115.89   $115.90   $115.90  
  7 purchase totals = $865.14       $941.4883   $941.49   $941.45   $941.60