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 $82.87   13.626%   $94.1619   $94.16   $94.15   $94.20  
  Purchase #2 $85.83   9.464%   $93.953   $93.95   $93.95   $94.00  
  Purchase #3 $7.79   13.200%   $8.8183   $8.82   $8.80   $8.80  
  Purchase #4 $12.41   8.706%   $13.4904   $13.49   $13.50   $13.50  
  Purchase #5 $152.48   5.474%   $160.8268   $160.83   $160.85   $160.80  
  Purchase #6 $205.96   9.831%   $226.2079   $226.21   $226.20   $226.20  
  Purchase #7 $73.77   13.508%   $83.7349   $83.73   $83.75   $83.70  
  7 purchase totals = $621.11       $681.1932   $681.19   $681.20   $681.20