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 $96.49   12.523%   $108.5734   $108.57   $108.55   $108.60  
  Purchase #2 $33.84   6.176%   $35.93   $35.93   $35.95   $35.90  
  Purchase #3 $143.64   8.619%   $156.0203   $156.02   $156.00   $156.00  
  Purchase #4 $137.88   8.148%   $149.1145   $149.11   $149.10   $149.10  
  Purchase #5 $61.56   12.664%   $69.356   $69.36   $69.35   $69.40  
  Purchase #6 $163.30   10.330%   $180.1689   $180.17   $180.15   $180.20  
  Purchase #7 $149.26   6.644%   $159.1768   $159.18   $159.20   $159.20  
  7 purchase totals = $785.97       $858.3399   $858.34   $858.30   $858.40