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 $107.75   12.569%   $121.2931   $121.29   $121.30   $121.30  
  Purchase #2 $168.85   9.336%   $184.6138   $184.61   $184.60   $184.60  
  Purchase #3 $66.85   3.273%   $69.038   $69.04   $69.05   $69.00  
  Purchase #4 $189.50   10.169%   $208.7703   $208.77   $208.75   $208.80  
  Purchase #5 $224.29   8.473%   $243.2941   $243.29   $243.30   $243.30  
  Purchase #6 $52.65   13.521%   $59.7688   $59.77   $59.75   $59.80  
  Purchase #7 $241.72   6.540%   $257.5285   $257.53   $257.55   $257.50  
  7 purchase totals = $1,051.61       $1,144.3066   $1,144.30   $1,144.30   $1,144.30