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 $66.69   10.576%   $73.7431   $73.74   $73.75   $73.70  
  Purchase #2 $27.80   6.817%   $29.6951   $29.70   $29.70   $29.70  
  Purchase #3 $86.94   7.347%   $93.3275   $93.33   $93.35   $93.30  
  Purchase #4 $243.56   11.390%   $271.3015   $271.30   $271.30   $271.30  
  Purchase #5 $172.34   9.561%   $188.8174   $188.82   $188.80   $188.80  
  Purchase #6 $67.83   10.727%   $75.1061   $75.11   $75.10   $75.10  
  Purchase #7 $46.59   9.836%   $51.1726   $51.17   $51.15   $51.20  
  7 purchase totals = $711.75       $783.1633   $783.17   $783.15   $783.10