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 $113.66   11.673%   $126.9275   $126.93   $126.95   $126.90  
  Purchase #2 $48.54   10.455%   $53.6149   $53.61   $53.60   $53.60  
  Purchase #3 $159.32   10.258%   $175.663   $175.66   $175.65   $175.70  
  Purchase #4 $122.64   10.616%   $135.6595   $135.66   $135.65   $135.70  
  Purchase #5 $162.96   4.134%   $169.6968   $169.70   $169.70   $169.70  
  Purchase #6 $167.93   3.794%   $174.3013   $174.30   $174.30   $174.30  
  Purchase #7 $65.29   4.336%   $68.121   $68.12   $68.10   $68.10  
  7 purchase totals = $840.34       $903.9840   $903.98   $903.95   $904.00