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 $87.44   8.214%   $94.6223   $94.62   $94.60   $94.60  
  Purchase #2 $209.59   7.522%   $225.3554   $225.36   $225.35   $225.40  
  Purchase #3 $99.40   4.796%   $104.1672   $104.17   $104.15   $104.20  
  Purchase #4 $42.81   5.418%   $45.1294   $45.13   $45.15   $45.10  
  Purchase #5 $191.25   6.774%   $204.2053   $204.21   $204.20   $204.20  
  Purchase #6 $168.86   8.564%   $183.3212   $183.32   $183.30   $183.30  
  Purchase #7 $139.68   4.598%   $146.1025   $146.10   $146.10   $146.10  
  7 purchase totals = $939.03       $1,002.9033   $1,002.91   $1,002.85   $1,002.90