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 $177.42   4.337%   $185.1147   $185.11   $185.10   $185.10  
  Purchase #2 $155.29   4.442%   $162.188   $162.19   $162.20   $162.20  
  Purchase #3 $81.26   3.374%   $84.0017   $84.00   $84.00   $84.00  
  Purchase #4 $33.61   8.324%   $36.4077   $36.41   $36.40   $36.40  
  Purchase #5 $100.49   5.751%   $106.2692   $106.27   $106.25   $106.30  
  Purchase #6 $138.71   7.394%   $148.9662   $148.97   $148.95   $149.00  
  Purchase #7 $139.59   13.294%   $158.1471   $158.15   $158.15   $158.10  
  7 purchase totals = $826.37       $881.0946   $881.10   $881.05   $881.10