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 $78.68   7.725%   $84.758   $84.76   $84.75   $84.80  
  Purchase #2 $247.32   3.605%   $256.2359   $256.24   $256.25   $256.20  
  Purchase #3 $22.83   9.805%   $25.0685   $25.07   $25.05   $25.10  
  Purchase #4 $249.93   7.784%   $269.3846   $269.38   $269.40   $269.40  
  Purchase #5 $85.90   5.441%   $90.5738   $90.57   $90.55   $90.60  
  Purchase #6 $10.97   7.644%   $11.8085   $11.81   $11.80   $11.80  
  Purchase #7 $36.67   12.298%   $41.1797   $41.18   $41.20   $41.20  
  7 purchase totals = $732.30       $779.0090   $779.01   $779.00   $779.10