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 $98.71   7.397%   $106.0116   $106.01   $106.00   $106.00  
  Purchase #2 $237.64   11.788%   $265.653   $265.65   $265.65   $265.70  
  Purchase #3 $228.26   13.408%   $258.8651   $258.87   $258.85   $258.90  
  Purchase #4 $220.75   10.273%   $243.4276   $243.43   $243.45   $243.40  
  Purchase #5 $242.58   11.841%   $271.3039   $271.30   $271.30   $271.30  
  Purchase #6 $190.39   4.635%   $199.2146   $199.21   $199.20   $199.20  
  Purchase #7 $66.88   12.403%   $75.1751   $75.18   $75.20   $75.20  
  7 purchase totals = $1,285.21       $1,419.6509   $1,419.65   $1,419.65   $1,419.70