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 $240.74   9.758%   $264.2314   $264.23   $264.25   $264.20  
  Purchase #2 $222.72   11.543%   $248.4286   $248.43   $248.45   $248.40  
  Purchase #3 $15.45   10.620%   $17.0908   $17.09   $17.10   $17.10  
  Purchase #4 $211.92   4.690%   $221.859   $221.86   $221.85   $221.90  
  Purchase #5 $43.88   6.541%   $46.7502   $46.75   $46.75   $46.80  
  Purchase #6 $50.61   10.728%   $56.0394   $56.04   $56.05   $56.00  
  Purchase #7 $184.59   9.347%   $201.8436   $201.84   $201.85   $201.80  
  7 purchase totals = $969.91       $1,056.2430   $1,056.24   $1,056.30   $1,056.20