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 $69.89   10.685%   $77.3577   $77.36   $77.35   $77.40  
  Purchase #2 $193.98   11.183%   $215.6728   $215.67   $215.65   $215.70  
  Purchase #3 $237.29   6.439%   $252.5691   $252.57   $252.55   $252.60  
  Purchase #4 $211.75   5.294%   $222.96   $222.96   $222.95   $223.00  
  Purchase #5 $174.99   11.400%   $194.9389   $194.94   $194.95   $194.90  
  Purchase #6 $160.47   11.181%   $178.4122   $178.41   $178.40   $178.40  
  Purchase #7 $126.97   5.429%   $133.8632   $133.86   $133.85   $133.90  
  7 purchase totals = $1,175.34       $1,275.7739   $1,275.77   $1,275.70   $1,275.90