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 $48.41   9.821%   $53.1643   $53.16   $53.15   $53.20  
  Purchase #2 $87.74   5.501%   $92.5666   $92.57   $92.55   $92.60  
  Purchase #3 $186.92   4.344%   $195.0398   $195.04   $195.05   $195.00  
  Purchase #4 $43.67   5.734%   $46.174   $46.17   $46.15   $46.20  
  Purchase #5 $100.25   10.699%   $110.9757   $110.98   $111.00   $111.00  
  Purchase #6 $176.70   12.811%   $199.337   $199.34   $199.35   $199.30  
  Purchase #7 $107.56   10.220%   $118.5526   $118.55   $118.55   $118.60  
  7 purchase totals = $751.25       $815.8100   $815.81   $815.80   $815.90