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 $231.39   13.498%   $262.623   $262.62   $262.60   $262.60  
  Purchase #2 $210.51   13.848%   $239.6614   $239.66   $239.65   $239.70  
  Purchase #3 $68.78   3.714%   $71.3345   $71.33   $71.35   $71.30  
  Purchase #4 $26.84   3.743%   $27.8446   $27.84   $27.85   $27.80  
  Purchase #5 $245.28   12.448%   $275.8125   $275.81   $275.80   $275.80  
  Purchase #6 $232.85   12.771%   $262.5873   $262.59   $262.60   $262.60  
  Purchase #7 $160.93   10.479%   $177.7939   $177.79   $177.80   $177.80  
  7 purchase totals = $1,176.58       $1,317.6572   $1,317.64   $1,317.65   $1,317.60