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 $24.52   3.521%   $25.3833   $25.38   $25.40   $25.40  
  Purchase #2 $249.53   11.170%   $277.4025   $277.40   $277.40   $277.40  
  Purchase #3 $32.89   5.514%   $34.7036   $34.70   $34.70   $34.70  
  Purchase #4 $55.73   12.279%   $62.5731   $62.57   $62.55   $62.60  
  Purchase #5 $170.77   3.440%   $176.6445   $176.64   $176.65   $176.60  
  Purchase #6 $182.49   13.407%   $206.9564   $206.96   $206.95   $207.00  
  Purchase #7 $25.88   3.307%   $26.7359   $26.74   $26.75   $26.70  
  7 purchase totals = $741.81       $810.3993   $810.39   $810.40   $810.40