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 $69.98   5.556%   $73.8681   $73.87   $73.85   $73.90  
  Purchase #2 $184.50   13.132%   $208.7285   $208.73   $208.75   $208.70  
  Purchase #3 $126.85   5.226%   $133.4792   $133.48   $133.50   $133.50  
  Purchase #4 $192.39   6.647%   $205.1782   $205.18   $205.20   $205.20  
  Purchase #5 $152.91   8.150%   $165.3722   $165.37   $165.35   $165.40  
  Purchase #6 $203.96   3.144%   $210.3725   $210.37   $210.35   $210.40  
  Purchase #7 $219.88   3.611%   $227.8199   $227.82   $227.80   $227.80  
  7 purchase totals = $1,150.47       $1,224.8186   $1,224.82   $1,224.80   $1,224.90