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 $56.96   7.552%   $61.2616   $61.26   $61.25   $61.30  
  Purchase #2 $130.42   10.156%   $143.6655   $143.67   $143.65   $143.70  
  Purchase #3 $65.71   4.814%   $68.8733   $68.87   $68.85   $68.90  
  Purchase #4 $155.29   3.449%   $160.646   $160.65   $160.65   $160.60  
  Purchase #5 $84.84   11.579%   $94.6636   $94.66   $94.65   $94.70  
  Purchase #6 $185.66   4.156%   $193.376   $193.38   $193.40   $193.40  
  Purchase #7 $173.84   8.754%   $189.058   $189.06   $189.05   $189.10  
  7 purchase totals = $852.72       $911.5440   $911.55   $911.50   $911.70