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 $61.33   5.663%   $64.8031   $64.80   $64.80   $64.80  
  Purchase #2 $109.53   9.497%   $119.9321   $119.93   $119.95   $119.90  
  Purchase #3 $205.83   5.253%   $216.6422   $216.64   $216.65   $216.60  
  Purchase #4 $193.62   6.593%   $206.3854   $206.39   $206.40   $206.40  
  Purchase #5 $196.57   7.521%   $211.354   $211.35   $211.35   $211.40  
  Purchase #6 $114.76   5.616%   $121.2049   $121.20   $121.20   $121.20  
  Purchase #7 $29.34   6.274%   $31.1808   $31.18   $31.20   $31.20  
  7 purchase totals = $910.98       $971.5025   $971.49   $971.55   $971.50