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 $214.83   13.115%   $243.005   $243.01   $243.00   $243.00  
  Purchase #2 $239.67   13.297%   $271.5389   $271.54   $271.55   $271.50  
  Purchase #3 $43.91   9.410%   $48.0419   $48.04   $48.05   $48.00  
  Purchase #4 $164.26   13.507%   $186.4466   $186.45   $186.45   $186.40  
  Purchase #5 $157.36   10.290%   $173.5523   $173.55   $173.55   $173.60  
  Purchase #6 $41.60   8.782%   $45.2533   $45.25   $45.25   $45.30  
  Purchase #7 $70.39   9.421%   $77.0214   $77.02   $77.00   $77.00  
  7 purchase totals = $932.02       $1,044.8594   $1,044.86   $1,044.85   $1,044.80