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 $175.39   10.827%   $194.3795   $194.38   $194.40   $194.40  
  Purchase #2 $98.91   6.833%   $105.6685   $105.67   $105.65   $105.70  
  Purchase #3 $120.35   12.829%   $135.7897   $135.79   $135.80   $135.80  
  Purchase #4 $247.31   4.477%   $258.3821   $258.38   $258.40   $258.40  
  Purchase #5 $34.32   3.460%   $35.5075   $35.51   $35.50   $35.50  
  Purchase #6 $18.71   3.839%   $19.4283   $19.43   $19.45   $19.40  
  Purchase #7 $8.88   3.303%   $9.1733   $9.17   $9.15   $9.20  
  7 purchase totals = $703.87       $758.3289   $758.33   $758.35   $758.40