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 $59.66   8.468%   $64.712   $64.71   $64.70   $64.70  
  Purchase #2 $73.45   13.857%   $83.628   $83.63   $83.65   $83.60  
  Purchase #3 $156.47   5.858%   $165.636   $165.64   $165.65   $165.60  
  Purchase #4 $32.85   4.416%   $34.3007   $34.30   $34.30   $34.30  
  Purchase #5 $160.95   12.536%   $181.1267   $181.13   $181.15   $181.10  
  Purchase #6 $107.59   5.139%   $113.1191   $113.12   $113.10   $113.10  
  Purchase #7 $208.96   10.292%   $230.4662   $230.47   $230.45   $230.50  
  7 purchase totals = $799.93       $872.9887   $873.00   $873.00   $872.90