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 $239.58   13.779%   $272.5917   $272.59   $272.60   $272.60  
  Purchase #2 $225.39   6.596%   $240.2567   $240.26   $240.25   $240.30  
  Purchase #3 $213.40   11.756%   $238.4873   $238.49   $238.50   $238.50  
  Purchase #4 $129.94   7.606%   $139.8232   $139.82   $139.80   $139.80  
  Purchase #5 $65.72   3.453%   $67.9893   $67.99   $68.00   $68.00  
  Purchase #6 $174.84   11.121%   $194.284   $194.28   $194.30   $194.30  
  Purchase #7 $201.34   3.797%   $208.9849   $208.98   $209.00   $209.00  
  7 purchase totals = $1,250.21       $1,362.4171   $1,362.41   $1,362.45   $1,362.50