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 $108.93   10.791%   $120.6846   $120.68   $120.70   $120.70  
  Purchase #2 $73.81   11.630%   $82.3941   $82.39   $82.40   $82.40  
  Purchase #3 $121.71   8.670%   $132.2623   $132.26   $132.25   $132.30  
  Purchase #4 $191.43   7.867%   $206.4898   $206.49   $206.50   $206.50  
  Purchase #5 $209.76   8.729%   $228.07   $228.07   $228.05   $228.10  
  Purchase #6 $237.96   5.391%   $250.7884   $250.79   $250.80   $250.80  
  Purchase #7 $5.66   7.784%   $6.1006   $6.10   $6.10   $6.10  
  7 purchase totals = $949.26       $1,026.7898   $1,026.78   $1,026.80   $1,026.90