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 $57.77   3.155%   $59.5926   $59.59   $59.60   $59.60  
  Purchase #2 $194.85   8.432%   $211.2798   $211.28   $211.30   $211.30  
  Purchase #3 $225.62   13.445%   $255.9546   $255.95   $255.95   $256.00  
  Purchase #4 $233.73   8.275%   $253.0712   $253.07   $253.05   $253.10  
  Purchase #5 $160.66   6.381%   $170.9117   $170.91   $170.90   $170.90  
  Purchase #6 $26.30   10.449%   $29.0481   $29.05   $29.05   $29.00  
  Purchase #7 $179.76   9.143%   $196.1955   $196.20   $196.20   $196.20  
  7 purchase totals = $1,078.69       $1,176.0535   $1,176.05   $1,176.05   $1,176.10