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 $62.77   13.769%   $71.4128   $71.41   $71.40   $71.40  
  Purchase #2 $88.70   4.831%   $92.9851   $92.99   $93.00   $93.00  
  Purchase #3 $213.30   3.715%   $221.2241   $221.22   $221.20   $221.20  
  Purchase #4 $83.65   11.502%   $93.2714   $93.27   $93.25   $93.30  
  Purchase #5 $195.65   12.447%   $220.0026   $220.00   $220.00   $220.00  
  Purchase #6 $67.31   8.569%   $73.0778   $73.08   $73.10   $73.10  
  Purchase #7 $218.98   10.296%   $241.5262   $241.53   $241.55   $241.50  
  7 purchase totals = $930.36       $1,013.5000   $1,013.50   $1,013.50   $1,013.50