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 $57.43   5.824%   $60.7747   $60.77   $60.75   $60.80  
  Purchase #2 $194.87   9.772%   $213.9127   $213.91   $213.90   $213.90  
  Purchase #3 $210.39   4.176%   $219.1759   $219.18   $219.20   $219.20  
  Purchase #4 $149.25   3.856%   $155.0051   $155.01   $155.00   $155.00  
  Purchase #5 $136.68   13.590%   $155.2548   $155.25   $155.25   $155.30  
  Purchase #6 $167.97   8.609%   $182.4305   $182.43   $182.45   $182.40  
  Purchase #7 $49.84   12.457%   $56.0486   $56.05   $56.05   $56.00  
  7 purchase totals = $966.43       $1,042.6023   $1,042.60   $1,042.60   $1,042.60