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 $188.81   12.239%   $211.9185   $211.92   $211.90   $211.90  
  Purchase #2 $92.87   8.715%   $100.9636   $100.96   $100.95   $101.00  
  Purchase #3 $161.88   5.273%   $170.4159   $170.42   $170.40   $170.40  
  Purchase #4 $172.76   12.443%   $194.2565   $194.26   $194.25   $194.30  
  Purchase #5 $104.85   12.115%   $117.5526   $117.55   $117.55   $117.60  
  Purchase #6 $235.99   4.234%   $245.9818   $245.98   $246.00   $246.00  
  Purchase #7 $24.73   7.134%   $26.4942   $26.49   $26.50   $26.50  
  7 purchase totals = $981.89       $1,067.5831   $1,067.58   $1,067.55   $1,067.70