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 $162.89   12.397%   $183.0835   $183.08   $183.10   $183.10  
  Purchase #2 $130.86   10.718%   $144.8856   $144.89   $144.90   $144.90  
  Purchase #3 $54.72   12.808%   $61.7285   $61.73   $61.75   $61.70  
  Purchase #4 $66.52   9.843%   $73.0676   $73.07   $73.05   $73.10  
  Purchase #5 $124.48   4.180%   $129.6833   $129.68   $129.70   $129.70  
  Purchase #6 $158.30   4.228%   $164.9929   $164.99   $165.00   $165.00  
  Purchase #7 $81.93   6.237%   $87.04   $87.04   $87.05   $87.00  
  7 purchase totals = $779.70       $844.4814   $844.48   $844.55   $844.50