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 $223.59   8.763%   $243.1832   $243.18   $243.20   $243.20  
  Purchase #2 $10.84   7.194%   $11.6198   $11.62   $11.60   $11.60  
  Purchase #3 $95.39   11.545%   $106.4028   $106.40   $106.40   $106.40  
  Purchase #4 $141.43   12.581%   $159.2233   $159.22   $159.20   $159.20  
  Purchase #5 $92.67   13.178%   $104.8821   $104.88   $104.90   $104.90  
  Purchase #6 $62.48   9.397%   $68.3512   $68.35   $68.35   $68.40  
  Purchase #7 $246.86   10.404%   $272.5433   $272.54   $272.55   $272.50  
  7 purchase totals = $873.26       $966.2057   $966.19   $966.20   $966.20