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 $191.61   4.532%   $200.2938   $200.29   $200.30   $200.30  
  Purchase #2 $225.66   11.821%   $252.3353   $252.34   $252.35   $252.30  
  Purchase #3 $204.81   9.282%   $223.8205   $223.82   $223.80   $223.80  
  Purchase #4 $32.76   9.139%   $35.7539   $35.75   $35.75   $35.80  
  Purchase #5 $220.68   13.121%   $249.6354   $249.64   $249.65   $249.60  
  Purchase #6 $125.90   12.488%   $141.6224   $141.62   $141.60   $141.60  
  Purchase #7 $174.49   10.136%   $192.1763   $192.18   $192.20   $192.20  
  7 purchase totals = $1,175.91       $1,295.6376   $1,295.64   $1,295.65   $1,295.60