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 $204.83   7.813%   $220.8334   $220.83   $220.85   $220.80  
  Purchase #2 $154.74   5.519%   $163.2801   $163.28   $163.30   $163.30  
  Purchase #3 $123.54   6.592%   $131.6838   $131.68   $131.70   $131.70  
  Purchase #4 $74.32   5.185%   $78.1735   $78.17   $78.15   $78.20  
  Purchase #5 $212.69   6.214%   $225.9066   $225.91   $225.90   $225.90  
  Purchase #6 $85.60   8.263%   $92.6731   $92.67   $92.65   $92.70  
  Purchase #7 $105.97   12.693%   $119.4208   $119.42   $119.40   $119.40  
  7 purchase totals = $961.69       $1,031.9713   $1,031.96   $1,031.95   $1,032.00