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 $54.93   10.477%   $60.685   $60.69   $60.70   $60.70  
  Purchase #2 $115.53   11.620%   $128.9546   $128.95   $128.95   $129.00  
  Purchase #3 $156.38   5.671%   $165.2483   $165.25   $165.25   $165.20  
  Purchase #4 $179.81   3.740%   $186.5349   $186.53   $186.55   $186.50  
  Purchase #5 $116.64   4.501%   $121.89   $121.89   $121.90   $121.90  
  Purchase #6 $73.37   5.314%   $77.2689   $77.27   $77.25   $77.30  
  Purchase #7 $174.41   9.817%   $191.5318   $191.53   $191.55   $191.50  
  7 purchase totals = $871.07       $932.1135   $932.11   $932.15   $932.10