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 $218.82   10.554%   $241.9143   $241.91   $241.90   $241.90  
  Purchase #2 $158.82   6.231%   $168.7161   $168.72   $168.70   $168.70  
  Purchase #3 $85.90   8.431%   $93.1422   $93.14   $93.15   $93.10  
  Purchase #4 $209.51   9.426%   $229.2584   $229.26   $229.25   $229.30  
  Purchase #5 $224.67   11.457%   $250.4104   $250.41   $250.40   $250.40  
  Purchase #6 $177.40   7.442%   $190.6021   $190.60   $190.60   $190.60  
  Purchase #7 $126.41   6.833%   $135.0476   $135.05   $135.05   $135.00  
  7 purchase totals = $1,201.53       $1,309.0911   $1,309.09   $1,309.05   $1,309.00