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 $56.52   11.709%   $63.1379   $63.14   $63.15   $63.10  
  Purchase #2 $199.46   4.692%   $208.8187   $208.82   $208.80   $208.80  
  Purchase #3 $215.83   8.393%   $233.9446   $233.94   $233.95   $233.90  
  Purchase #4 $95.64   3.282%   $98.7789   $98.78   $98.80   $98.80  
  Purchase #5 $219.36   11.371%   $244.3034   $244.30   $244.30   $244.30  
  Purchase #6 $95.84   12.363%   $107.6887   $107.69   $107.70   $107.70  
  Purchase #7 $214.70   12.199%   $240.8913   $240.89   $240.90   $240.90  
  7 purchase totals = $1,097.35       $1,197.5635   $1,197.56   $1,197.60   $1,197.50