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 $205.31   13.803%   $233.6489   $233.65   $233.65   $233.60  
  Purchase #2 $15.96   11.565%   $17.8058   $17.81   $17.80   $17.80  
  Purchase #3 $49.47   4.149%   $51.5225   $51.52   $51.50   $51.50  
  Purchase #4 $124.83   6.453%   $132.8853   $132.89   $132.90   $132.90  
  Purchase #5 $142.90   11.825%   $159.7979   $159.80   $159.80   $159.80  
  Purchase #6 $126.61   9.706%   $138.8988   $138.90   $138.90   $138.90  
  Purchase #7 $197.71   10.656%   $218.778   $218.78   $218.80   $218.80  
  7 purchase totals = $862.79       $953.3372   $953.35   $953.35   $953.30