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 $213.77   12.728%   $240.9786   $240.98   $241.00   $241.00  
  Purchase #2 $162.70   13.654%   $184.9151   $184.92   $184.90   $184.90  
  Purchase #3 $87.47   5.457%   $92.2432   $92.24   $92.25   $92.20  
  Purchase #4 $43.90   3.771%   $45.5555   $45.56   $45.55   $45.60  
  Purchase #5 $69.87   7.491%   $75.104   $75.10   $75.10   $75.10  
  Purchase #6 $140.40   8.807%   $152.765   $152.77   $152.75   $152.80  
  Purchase #7 $115.79   5.466%   $122.1191   $122.12   $122.10   $122.10  
  7 purchase totals = $833.90       $913.6805   $913.69   $913.65   $913.70