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 $127.85   6.117%   $135.6706   $135.67   $135.65   $135.70  
  Purchase #2 $144.96   4.180%   $151.0193   $151.02   $151.00   $151.00  
  Purchase #3 $39.78   9.333%   $43.4927   $43.49   $43.50   $43.50  
  Purchase #4 $232.86   5.329%   $245.2691   $245.27   $245.25   $245.30  
  Purchase #5 $120.28   10.524%   $132.9383   $132.94   $132.95   $132.90  
  Purchase #6 $247.66   4.807%   $259.565   $259.57   $259.55   $259.60  
  Purchase #7 $32.84   6.551%   $34.9913   $34.99   $35.00   $35.00  
  7 purchase totals = $946.23       $1,002.9463   $1,002.95   $1,002.90   $1,003.00