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 $118.36   7.431%   $127.1553   $127.16   $127.15   $127.20  
  Purchase #2 $246.50   6.555%   $262.6581   $262.66   $262.65   $262.70  
  Purchase #3 $49.44   5.574%   $52.1958   $52.20   $52.20   $52.20  
  Purchase #4 $217.42   10.815%   $240.934   $240.93   $240.95   $240.90  
  Purchase #5 $7.42   6.806%   $7.925   $7.93   $7.95   $7.90  
  Purchase #6 $168.80   13.731%   $191.9779   $191.98   $192.00   $192.00  
  Purchase #7 $19.61   4.725%   $20.5366   $20.54   $20.55   $20.50  
  7 purchase totals = $827.55       $903.3827   $903.40   $903.45   $903.40