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 $246.75   10.845%   $273.51   $273.51   $273.50   $273.50  
  Purchase #2 $83.95   5.720%   $88.7519   $88.75   $88.75   $88.80  
  Purchase #3 $162.38   7.658%   $174.8151   $174.82   $174.80   $174.80  
  Purchase #4 $196.64   7.340%   $211.0734   $211.07   $211.05   $211.10  
  Purchase #5 $115.31   6.406%   $122.6968   $122.70   $122.70   $122.70  
  Purchase #6 $60.97   5.288%   $64.1941   $64.19   $64.20   $64.20  
  Purchase #7 $169.92   3.747%   $176.2869   $176.29   $176.30   $176.30  
  7 purchase totals = $1,035.92       $1,111.3282   $1,111.33   $1,111.30   $1,111.40