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 $227.43   5.568%   $240.0933   $240.09   $240.10   $240.10  
  Purchase #2 $55.82   11.651%   $62.3236   $62.32   $62.30   $62.30  
  Purchase #3 $164.70   5.788%   $174.2328   $174.23   $174.25   $174.20  
  Purchase #4 $110.54   7.493%   $118.8228   $118.82   $118.80   $118.80  
  Purchase #5 $120.37   8.752%   $130.9048   $130.90   $130.90   $130.90  
  Purchase #6 $163.83   6.780%   $174.9377   $174.94   $174.95   $174.90  
  Purchase #7 $33.47   5.283%   $35.2382   $35.24   $35.25   $35.20  
  7 purchase totals = $876.16       $936.5532   $936.54   $936.55   $936.40