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 $79.91   7.602%   $85.9848   $85.98   $86.00   $86.00  
  Purchase #2 $58.69   10.113%   $64.6253   $64.63   $64.65   $64.60  
  Purchase #3 $249.34   13.577%   $283.1929   $283.19   $283.20   $283.20  
  Purchase #4 $44.42   7.785%   $47.8781   $47.88   $47.90   $47.90  
  Purchase #5 $161.47   6.865%   $172.5549   $172.55   $172.55   $172.60  
  Purchase #6 $41.50   13.341%   $47.0365   $47.04   $47.05   $47.00  
  Purchase #7 $210.49   8.771%   $228.9521   $228.95   $228.95   $229.00  
  7 purchase totals = $845.82       $930.2246   $930.22   $930.30   $930.30