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 $230.75   12.696%   $260.046   $260.05   $260.05   $260.00  
  Purchase #2 $160.84   9.234%   $175.692   $175.69   $175.70   $175.70  
  Purchase #3 $133.99   11.455%   $149.3386   $149.34   $149.35   $149.30  
  Purchase #4 $210.49   9.499%   $230.4844   $230.48   $230.50   $230.50  
  Purchase #5 $227.29   3.754%   $235.8225   $235.82   $235.80   $235.80  
  Purchase #6 $82.45   3.872%   $85.6425   $85.64   $85.65   $85.60  
  Purchase #7 $70.98   9.442%   $77.6819   $77.68   $77.70   $77.70  
  7 purchase totals = $1,116.79       $1,214.7079   $1,214.70   $1,214.75   $1,214.60