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 $34.68   4.695%   $36.3082   $36.31   $36.30   $36.30  
  Purchase #2 $241.66   7.463%   $259.6951   $259.70   $259.70   $259.70  
  Purchase #3 $136.66   9.184%   $149.2109   $149.21   $149.20   $149.20  
  Purchase #4 $26.93   11.566%   $30.0447   $30.04   $30.05   $30.00  
  Purchase #5 $128.42   7.340%   $137.846   $137.85   $137.85   $137.80  
  Purchase #6 $212.62   11.162%   $236.3526   $236.35   $236.35   $236.40  
  Purchase #7 $164.91   6.317%   $175.3274   $175.33   $175.35   $175.30  
  7 purchase totals = $945.88       $1,024.7849   $1,024.79   $1,024.80   $1,024.70