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 $229.33   9.441%   $250.981   $250.98   $251.00   $251.00  
  Purchase #2 $147.34   11.446%   $164.2045   $164.20   $164.20   $164.20  
  Purchase #3 $107.50   11.153%   $119.4895   $119.49   $119.50   $119.50  
  Purchase #4 $28.71   13.182%   $32.4946   $32.49   $32.50   $32.50  
  Purchase #5 $204.55   7.497%   $219.8851   $219.89   $219.90   $219.90  
  Purchase #6 $120.99   5.492%   $127.6348   $127.63   $127.65   $127.60  
  Purchase #7 $129.75   12.644%   $146.1556   $146.16   $146.15   $146.20  
  7 purchase totals = $968.17       $1,060.8451   $1,060.84   $1,060.90   $1,060.90