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 $62.74   5.640%   $66.2785   $66.28   $66.30   $66.30  
  Purchase #2 $245.66   11.459%   $273.8102   $273.81   $273.80   $273.80  
  Purchase #3 $84.40   12.155%   $94.6588   $94.66   $94.65   $94.70  
  Purchase #4 $250.95   9.157%   $273.9295   $273.93   $273.95   $273.90  
  Purchase #5 $46.86   9.576%   $51.3473   $51.35   $51.35   $51.30  
  Purchase #6 $246.96   10.426%   $272.708   $272.71   $272.70   $272.70  
  Purchase #7 $97.89   3.687%   $101.4992   $101.50   $101.50   $101.50  
  7 purchase totals = $1,035.46       $1,134.2315   $1,134.24   $1,134.25   $1,134.20