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 $64.98   12.778%   $73.2831   $73.28   $73.30   $73.30  
  Purchase #2 $119.61   5.601%   $126.3094   $126.31   $126.30   $126.30  
  Purchase #3 $194.48   6.325%   $206.7809   $206.78   $206.80   $206.80  
  Purchase #4 $46.38   12.516%   $52.1849   $52.18   $52.20   $52.20  
  Purchase #5 $7.27   11.872%   $8.1331   $8.13   $8.15   $8.10  
  Purchase #6 $83.49   11.381%   $92.992   $92.99   $93.00   $93.00  
  Purchase #7 $54.35   12.687%   $61.2454   $61.25   $61.25   $61.20  
  7 purchase totals = $570.56       $620.9288   $620.92   $621.00   $620.90