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 $243.98   6.662%   $260.2339   $260.23   $260.25   $260.20  
  Purchase #2 $66.88   9.185%   $73.0229   $73.02   $73.00   $73.00  
  Purchase #3 $163.99   5.677%   $173.2997   $173.30   $173.30   $173.30  
  Purchase #4 $212.53   6.515%   $226.3763   $226.38   $226.40   $226.40  
  Purchase #5 $72.68   6.664%   $77.5234   $77.52   $77.50   $77.50  
  Purchase #6 $173.77   12.530%   $195.5434   $195.54   $195.55   $195.50  
  Purchase #7 $161.53   11.561%   $180.2045   $180.20   $180.20   $180.20  
  7 purchase totals = $1,095.36       $1,186.2041   $1,186.19   $1,186.20   $1,186.10