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 $57.57   7.649%   $61.9735   $61.97   $61.95   $62.00  
  Purchase #2 $194.44   12.764%   $219.2583   $219.26   $219.25   $219.30  
  Purchase #3 $37.37   4.698%   $39.1256   $39.13   $39.15   $39.10  
  Purchase #4 $74.88   6.681%   $79.8827   $79.88   $79.90   $79.90  
  Purchase #5 $194.99   12.595%   $219.549   $219.55   $219.55   $219.50  
  Purchase #6 $191.51   11.296%   $213.143   $213.14   $213.15   $213.10  
  Purchase #7 $47.34   6.846%   $50.5809   $50.58   $50.60   $50.60  
  7 purchase totals = $798.10       $883.5130   $883.51   $883.55   $883.50