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 $64.98   8.866%   $70.7411   $70.74   $70.75   $70.70  
  Purchase #2 $181.25   11.688%   $202.4345   $202.43   $202.45   $202.40  
  Purchase #3 $233.57   11.770%   $261.0612   $261.06   $261.05   $261.10  
  Purchase #4 $208.46   6.449%   $221.9036   $221.90   $221.90   $221.90  
  Purchase #5 $123.33   10.702%   $136.5288   $136.53   $136.55   $136.50  
  Purchase #6 $41.45   13.256%   $46.9446   $46.94   $46.95   $46.90  
  Purchase #7 $83.34   13.600%   $94.6742   $94.67   $94.65   $94.70  
  7 purchase totals = $936.38       $1,034.2880   $1,034.27   $1,034.30   $1,034.20