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 $240.81   13.657%   $273.6974   $273.70   $273.70   $273.70  
  Purchase #2 $54.51   9.284%   $59.5707   $59.57   $59.55   $59.60  
  Purchase #3 $32.45   5.299%   $34.1695   $34.17   $34.15   $34.20  
  Purchase #4 $29.41   6.809%   $31.4125   $31.41   $31.40   $31.40  
  Purchase #5 $169.33   4.711%   $177.3071   $177.31   $177.30   $177.30  
  Purchase #6 $162.79   3.873%   $169.0949   $169.09   $169.10   $169.10  
  Purchase #7 $185.76   11.107%   $206.3924   $206.39   $206.40   $206.40  
  7 purchase totals = $875.06       $951.6445   $951.64   $951.60   $951.70