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 $217.49   13.542%   $246.9425   $246.94   $246.95   $246.90  
  Purchase #2 $233.44   3.417%   $241.4166   $241.42   $241.40   $241.40  
  Purchase #3 $69.40   3.757%   $72.0074   $72.01   $72.00   $72.00  
  Purchase #4 $108.91   13.272%   $123.3645   $123.36   $123.35   $123.40  
  Purchase #5 $204.76   3.122%   $211.1526   $211.15   $211.15   $211.20  
  Purchase #6 $126.27   5.288%   $132.9472   $132.95   $132.95   $132.90  
  Purchase #7 $88.84   12.444%   $99.8952   $99.90   $99.90   $99.90  
  7 purchase totals = $1,049.11       $1,127.7260   $1,127.73   $1,127.70   $1,127.70