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 $201.47   9.169%   $219.9428   $219.94   $219.95   $219.90  
  Purchase #2 $200.25   3.275%   $206.8082   $206.81   $206.80   $206.80  
  Purchase #3 $12.65   7.459%   $13.5936   $13.59   $13.60   $13.60  
  Purchase #4 $114.86   8.479%   $124.599   $124.60   $124.60   $124.60  
  Purchase #5 $115.99   9.518%   $127.0299   $127.03   $127.05   $127.00  
  Purchase #6 $150.75   11.637%   $168.2928   $168.29   $168.30   $168.30  
  Purchase #7 $98.59   8.540%   $107.0096   $107.01   $107.00   $107.00  
  7 purchase totals = $894.56       $967.2759   $967.27   $967.30   $967.20