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 $114.65   8.812%   $124.753   $124.75   $124.75   $124.80  
  Purchase #2 $108.39   4.838%   $113.6339   $113.63   $113.65   $113.60  
  Purchase #3 $221.35   9.354%   $242.0551   $242.06   $242.05   $242.10  
  Purchase #4 $250.57   5.651%   $264.7297   $264.73   $264.75   $264.70  
  Purchase #5 $223.54   12.477%   $251.4311   $251.43   $251.45   $251.40  
  Purchase #6 $243.97   9.856%   $268.0157   $268.02   $268.00   $268.00  
  Purchase #7 $32.51   9.754%   $35.681   $35.68   $35.70   $35.70  
  7 purchase totals = $1,194.98       $1,300.2995   $1,300.30   $1,300.35   $1,300.30