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 $60.94   13.290%   $69.0389   $69.04   $69.05   $69.00  
  Purchase #2 $172.56   10.603%   $190.8565   $190.86   $190.85   $190.90  
  Purchase #3 $31.89   3.764%   $33.0903   $33.09   $33.10   $33.10  
  Purchase #4 $125.90   11.584%   $140.4843   $140.48   $140.50   $140.50  
  Purchase #5 $24.81   4.644%   $25.9622   $25.96   $25.95   $26.00  
  Purchase #6 $197.55   8.792%   $214.9186   $214.92   $214.90   $214.90  
  Purchase #7 $13.43   12.224%   $15.0717   $15.07   $15.05   $15.10  
  7 purchase totals = $627.08       $689.4225   $689.42   $689.40   $689.50