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 $61.69   10.506%   $68.1712   $68.17   $68.15   $68.20  
  Purchase #2 $239.59   11.179%   $266.3738   $266.37   $266.35   $266.40  
  Purchase #3 $130.47   7.868%   $140.7354   $140.74   $140.75   $140.70  
  Purchase #4 $210.34   9.652%   $230.642   $230.64   $230.65   $230.60  
  Purchase #5 $237.49   3.483%   $245.7618   $245.76   $245.75   $245.80  
  Purchase #6 $199.82   11.374%   $222.5475   $222.55   $222.55   $222.50  
  Purchase #7 $47.78   12.553%   $53.7778   $53.78   $53.80   $53.80  
  7 purchase totals = $1,127.18       $1,228.0095   $1,228.01   $1,228.00   $1,228.00