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 $85.42   3.838%   $88.6984   $88.70   $88.70   $88.70  
  Purchase #2 $121.90   10.833%   $135.1054   $135.11   $135.10   $135.10  
  Purchase #3 $176.72   12.216%   $198.3081   $198.31   $198.30   $198.30  
  Purchase #4 $248.25   11.431%   $276.6275   $276.63   $276.65   $276.60  
  Purchase #5 $87.42   8.624%   $94.9591   $94.96   $94.95   $95.00  
  Purchase #6 $33.63   5.145%   $35.3603   $35.36   $35.35   $35.40  
  Purchase #7 $244.37   8.637%   $265.4762   $265.48   $265.50   $265.50  
  7 purchase totals = $997.71       $1,094.5350   $1,094.55   $1,094.55   $1,094.60