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 $61.63   7.608%   $66.3188   $66.32   $66.30   $66.30  
  Purchase #2 $175.46   6.722%   $187.2544   $187.25   $187.25   $187.30  
  Purchase #3 $197.50   13.812%   $224.7787   $224.78   $224.80   $224.80  
  Purchase #4 $211.64   10.524%   $233.913   $233.91   $233.90   $233.90  
  Purchase #5 $146.45   5.180%   $154.0361   $154.04   $154.05   $154.00  
  Purchase #6 $27.96   3.805%   $29.0239   $29.02   $29.00   $29.00  
  Purchase #7 $223.72   6.191%   $237.5705   $237.57   $237.55   $237.60  
  7 purchase totals = $1,044.36       $1,132.8954   $1,132.89   $1,132.85   $1,132.90