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 $209.26   8.485%   $227.0157   $227.02   $227.00   $227.00  
  Purchase #2 $168.71   6.184%   $179.143   $179.14   $179.15   $179.10  
  Purchase #3 $101.82   6.614%   $108.5544   $108.55   $108.55   $108.60  
  Purchase #4 $22.29   9.550%   $24.4187   $24.42   $24.40   $24.40  
  Purchase #5 $128.53   6.321%   $136.6544   $136.65   $136.65   $136.70  
  Purchase #6 $63.49   8.446%   $68.8524   $68.85   $68.85   $68.90  
  Purchase #7 $187.53   6.873%   $200.4189   $200.42   $200.40   $200.40  
  7 purchase totals = $881.63       $945.0575   $945.05   $945.00   $945.10