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 $92.99   3.218%   $95.9824   $95.98   $96.00   $96.00  
  Purchase #2 $154.90   3.833%   $160.8373   $160.84   $160.85   $160.80  
  Purchase #3 $23.64   4.712%   $24.7539   $24.75   $24.75   $24.80  
  Purchase #4 $23.45   3.137%   $24.1856   $24.19   $24.20   $24.20  
  Purchase #5 $134.83   12.496%   $151.6784   $151.68   $151.70   $151.70  
  Purchase #6 $188.58   13.679%   $214.3759   $214.38   $214.40   $214.40  
  Purchase #7 $180.80   13.360%   $204.9549   $204.95   $204.95   $205.00  
  7 purchase totals = $799.19       $876.7684   $876.77   $876.85   $876.90