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 $222.27   9.218%   $242.7588   $242.76   $242.75   $242.80  
  Purchase #2 $97.52   13.399%   $110.5867   $110.59   $110.60   $110.60  
  Purchase #3 $79.28   3.509%   $82.0619   $82.06   $82.05   $82.10  
  Purchase #4 $162.33   11.677%   $181.2853   $181.29   $181.30   $181.30  
  Purchase #5 $57.25   5.784%   $60.5613   $60.56   $60.55   $60.60  
  Purchase #6 $68.83   8.117%   $74.4169   $74.42   $74.40   $74.40  
  Purchase #7 $222.34   8.121%   $240.3962   $240.40   $240.40   $240.40  
  7 purchase totals = $909.82       $992.0671   $992.08   $992.05   $992.20