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 $66.84   10.574%   $73.9077   $73.91   $73.90   $73.90  
  Purchase #2 $188.58   4.245%   $196.5852   $196.59   $196.60   $196.60  
  Purchase #3 $165.89   6.762%   $177.1075   $177.11   $177.10   $177.10  
  Purchase #4 $111.29   5.813%   $117.7593   $117.76   $117.75   $117.80  
  Purchase #5 $41.56   7.215%   $44.5586   $44.56   $44.55   $44.60  
  Purchase #6 $193.78   4.104%   $201.7327   $201.73   $201.75   $201.70  
  Purchase #7 $116.52   9.505%   $127.5952   $127.60   $127.60   $127.60  
  7 purchase totals = $884.46       $939.2462   $939.26   $939.25   $939.30