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 $211.34   9.326%   $231.0496   $231.05   $231.05   $231.00  
  Purchase #2 $94.72   10.115%   $104.3009   $104.30   $104.30   $104.30  
  Purchase #3 $44.57   12.194%   $50.0049   $50.00   $50.00   $50.00  
  Purchase #4 $171.74   9.685%   $188.373   $188.37   $188.35   $188.40  
  Purchase #5 $83.60   5.472%   $88.1746   $88.17   $88.15   $88.20  
  Purchase #6 $195.87   12.846%   $221.0315   $221.03   $221.05   $221.00  
  Purchase #7 $80.38   3.325%   $83.0526   $83.05   $83.05   $83.10  
  7 purchase totals = $882.22       $965.9871   $965.97   $965.95   $966.00