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 $203.47   13.164%   $230.2548   $230.25   $230.25   $230.30  
  Purchase #2 $132.64   13.859%   $151.0226   $151.02   $151.00   $151.00  
  Purchase #3 $222.32   9.516%   $243.476   $243.48   $243.50   $243.50  
  Purchase #4 $200.58   9.227%   $219.0875   $219.09   $219.10   $219.10  
  Purchase #5 $217.36   3.366%   $224.6763   $224.68   $224.70   $224.70  
  Purchase #6 $209.53   12.732%   $236.2074   $236.21   $236.20   $236.20  
  Purchase #7 $51.45   11.270%   $57.2484   $57.25   $57.25   $57.20  
  7 purchase totals = $1,237.35       $1,361.9730   $1,361.98   $1,362.00   $1,362.00