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 $241.63   12.658%   $272.2155   $272.22   $272.20   $272.20  
  Purchase #2 $149.38   8.124%   $161.5156   $161.52   $161.50   $161.50  
  Purchase #3 $45.33   13.362%   $51.387   $51.39   $51.40   $51.40  
  Purchase #4 $180.91   9.221%   $197.5917   $197.59   $197.60   $197.60  
  Purchase #5 $247.90   11.580%   $276.6068   $276.61   $276.60   $276.60  
  Purchase #6 $97.90   12.743%   $110.3754   $110.38   $110.40   $110.40  
  Purchase #7 $57.96   3.653%   $60.0773   $60.08   $60.10   $60.10  
  7 purchase totals = $1,021.01       $1,129.7693   $1,129.79   $1,129.80   $1,129.80