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 $34.57   8.188%   $37.4006   $37.40   $37.40   $37.40  
  Purchase #2 $56.73   4.599%   $59.339   $59.34   $59.35   $59.30  
  Purchase #3 $97.47   7.840%   $105.1116   $105.11   $105.10   $105.10  
  Purchase #4 $166.75   6.694%   $177.9122   $177.91   $177.90   $177.90  
  Purchase #5 $148.34   8.103%   $160.36   $160.36   $160.35   $160.40  
  Purchase #6 $24.56   12.794%   $27.7022   $27.70   $27.70   $27.70  
  Purchase #7 $244.69   6.321%   $260.1569   $260.16   $260.15   $260.20  
  7 purchase totals = $773.11       $827.9825   $827.98   $827.95   $828.00