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 $236.48   9.616%   $259.2199   $259.22   $259.20   $259.20  
  Purchase #2 $138.97   7.524%   $149.4261   $149.43   $149.45   $149.40  
  Purchase #3 $204.44   12.590%   $230.179   $230.18   $230.20   $230.20  
  Purchase #4 $242.32   6.386%   $257.7946   $257.79   $257.80   $257.80  
  Purchase #5 $73.73   3.395%   $76.2331   $76.23   $76.25   $76.20  
  Purchase #6 $148.96   7.429%   $160.0262   $160.03   $160.05   $160.00  
  Purchase #7 $229.45   3.194%   $236.7786   $236.78   $236.80   $236.80  
  7 purchase totals = $1,274.35       $1,369.6575   $1,369.66   $1,369.75   $1,369.60