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 $55.39   10.201%   $61.0403   $61.04   $61.05   $61.00  
  Purchase #2 $194.61   11.165%   $216.3382   $216.34   $216.35   $216.30  
  Purchase #3 $34.85   10.489%   $38.5054   $38.51   $38.50   $38.50  
  Purchase #4 $56.39   8.218%   $61.0241   $61.02   $61.00   $61.00  
  Purchase #5 $150.32   6.290%   $159.7751   $159.78   $159.80   $159.80  
  Purchase #6 $171.98   8.412%   $186.447   $186.45   $186.45   $186.40  
  Purchase #7 $7.76   5.639%   $8.1976   $8.20   $8.20   $8.20  
  7 purchase totals = $671.30       $731.3277   $731.34   $731.35   $731.20