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 $84.53   9.164%   $92.2763   $92.28   $92.30   $92.30  
  Purchase #2 $250.79   7.636%   $269.9403   $269.94   $269.95   $269.90  
  Purchase #3 $90.73   4.734%   $95.0252   $95.03   $95.05   $95.00  
  Purchase #4 $88.86   3.124%   $91.636   $91.64   $91.65   $91.60  
  Purchase #5 $218.32   5.379%   $230.0634   $230.06   $230.05   $230.10  
  Purchase #6 $241.79   13.340%   $274.0448   $274.04   $274.05   $274.00  
  Purchase #7 $40.60   10.281%   $44.7741   $44.77   $44.75   $44.80  
  7 purchase totals = $1,015.62       $1,097.7601   $1,097.76   $1,097.80   $1,097.70