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 $124.49   9.778%   $136.6626   $136.66   $136.65   $136.70  
  Purchase #2 $134.57   6.240%   $142.9672   $142.97   $142.95   $143.00  
  Purchase #3 $238.44   6.717%   $254.456   $254.46   $254.45   $254.50  
  Purchase #4 $58.79   3.145%   $60.6389   $60.64   $60.65   $60.60  
  Purchase #5 $209.80   6.142%   $222.6859   $222.69   $222.70   $222.70  
  Purchase #6 $95.78   10.258%   $105.6051   $105.61   $105.60   $105.60  
  Purchase #7 $56.74   3.156%   $58.5307   $58.53   $58.55   $58.50  
  7 purchase totals = $918.61       $981.5464   $981.56   $981.55   $981.60