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 $250.47   5.105%   $263.2565   $263.26   $263.25   $263.30  
  Purchase #2 $211.87   11.265%   $235.7372   $235.74   $235.75   $235.70  
  Purchase #3 $19.35   3.372%   $20.0025   $20.00   $20.00   $20.00  
  Purchase #4 $249.94   4.107%   $260.205   $260.21   $260.20   $260.20  
  Purchase #5 $174.76   6.472%   $186.0705   $186.07   $186.05   $186.10  
  Purchase #6 $58.91   3.874%   $61.1922   $61.19   $61.20   $61.20  
  Purchase #7 $187.84   8.511%   $203.8271   $203.83   $203.85   $203.80  
  7 purchase totals = $1,153.14       $1,230.2910   $1,230.30   $1,230.30   $1,230.30