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 $58.60   13.591%   $66.5643   $66.56   $66.55   $66.60  
  Purchase #2 $191.50   11.755%   $214.0108   $214.01   $214.00   $214.00  
  Purchase #3 $161.39   10.815%   $178.8443   $178.84   $178.85   $178.80  
  Purchase #4 $117.90   6.436%   $125.488   $125.49   $125.50   $125.50  
  Purchase #5 $64.74   9.415%   $70.8353   $70.84   $70.85   $70.80  
  Purchase #6 $209.86   3.431%   $217.0603   $217.06   $217.05   $217.10  
  Purchase #7 $165.61   13.357%   $187.7305   $187.73   $187.75   $187.70  
  7 purchase totals = $969.60       $1,060.5335   $1,060.53   $1,060.55   $1,060.50