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 $95.97   11.678%   $107.1774   $107.18   $107.20   $107.20  
  Purchase #2 $171.68   12.211%   $192.6438   $192.64   $192.65   $192.60  
  Purchase #3 $148.96   3.254%   $153.8072   $153.81   $153.80   $153.80  
  Purchase #4 $86.98   8.707%   $94.5533   $94.55   $94.55   $94.60  
  Purchase #5 $157.54   12.154%   $176.6874   $176.69   $176.70   $176.70  
  Purchase #6 $74.56   9.131%   $81.3681   $81.37   $81.35   $81.40  
  Purchase #7 $210.98   12.616%   $237.5972   $237.60   $237.60   $237.60  
  7 purchase totals = $946.67       $1,043.8344   $1,043.84   $1,043.85   $1,043.90