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 $54.67   8.633%   $59.3897   $59.39   $59.40   $59.40  
  Purchase #2 $173.95   12.166%   $195.1128   $195.11   $195.10   $195.10  
  Purchase #3 $224.45   7.721%   $241.7798   $241.78   $241.80   $241.80  
  Purchase #4 $214.27   6.170%   $227.4905   $227.49   $227.50   $227.50  
  Purchase #5 $50.64   5.674%   $53.5133   $53.51   $53.50   $53.50  
  Purchase #6 $26.31   8.575%   $28.5661   $28.57   $28.55   $28.60  
  Purchase #7 $17.77   7.386%   $19.0825   $19.08   $19.10   $19.10  
  7 purchase totals = $762.06       $824.9347   $824.93   $824.95   $825.00