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 $208.33   4.636%   $217.9882   $217.99   $218.00   $218.00  
  Purchase #2 $240.97   11.631%   $268.9972   $269.00   $269.00   $269.00  
  Purchase #3 $170.69   12.410%   $191.8726   $191.87   $191.85   $191.90  
  Purchase #4 $195.69   11.308%   $217.8186   $217.82   $217.80   $217.80  
  Purchase #5 $249.57   9.442%   $273.1344   $273.13   $273.15   $273.10  
  Purchase #6 $220.29   10.395%   $243.1891   $243.19   $243.20   $243.20  
  Purchase #7 $150.61   6.679%   $160.6692   $160.67   $160.65   $160.70  
  7 purchase totals = $1,436.15       $1,573.6693   $1,573.67   $1,573.65   $1,573.70