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 $237.39   8.482%   $257.5254   $257.53   $257.55   $257.50  
  Purchase #2 $26.39   7.669%   $28.4138   $28.41   $28.40   $28.40  
  Purchase #3 $25.56   3.545%   $26.4661   $26.47   $26.45   $26.50  
  Purchase #4 $178.68   11.564%   $199.3426   $199.34   $199.35   $199.30  
  Purchase #5 $184.29   11.676%   $205.8077   $205.81   $205.80   $205.80  
  Purchase #6 $49.39   6.328%   $52.5154   $52.52   $52.50   $52.50  
  Purchase #7 $229.54   3.132%   $236.7292   $236.73   $236.75   $236.70  
  7 purchase totals = $931.24       $1,006.8002   $1,006.81   $1,006.80   $1,006.70