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 $244.76   9.212%   $267.3073   $267.31   $267.30   $267.30  
  Purchase #2 $120.87   8.154%   $130.7257   $130.73   $130.75   $130.70  
  Purchase #3 $43.84   7.663%   $47.1995   $47.20   $47.20   $47.20  
  Purchase #4 $228.75   4.544%   $239.1444   $239.14   $239.15   $239.10  
  Purchase #5 $14.26   11.202%   $15.8574   $15.86   $15.85   $15.90  
  Purchase #6 $192.29   12.649%   $216.6128   $216.61   $216.60   $216.60  
  Purchase #7 $205.42   11.804%   $229.6678   $229.67   $229.65   $229.70  
  7 purchase totals = $1,050.19       $1,146.5149   $1,146.52   $1,146.50   $1,146.50