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 $238.29   11.743%   $266.2724   $266.27   $266.25   $266.30  
  Purchase #2 $85.54   3.791%   $88.7828   $88.78   $88.80   $88.80  
  Purchase #3 $227.80   5.807%   $241.0283   $241.03   $241.05   $241.00  
  Purchase #4 $158.96   5.754%   $168.1066   $168.11   $168.10   $168.10  
  Purchase #5 $211.40   10.237%   $233.041   $233.04   $233.05   $233.00  
  Purchase #6 $214.98   13.271%   $243.51   $243.51   $243.50   $243.50  
  Purchase #7 $149.52   11.218%   $166.2932   $166.29   $166.30   $166.30  
  7 purchase totals = $1,286.49       $1,407.0343   $1,407.03   $1,407.05   $1,407.00