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 $61.84   8.871%   $67.3258   $67.33   $67.35   $67.30  
  Purchase #2 $114.59   3.601%   $118.7164   $118.72   $118.70   $118.70  
  Purchase #3 $166.37   7.530%   $178.8977   $178.90   $178.90   $178.90  
  Purchase #4 $236.97   7.298%   $254.2641   $254.26   $254.25   $254.30  
  Purchase #5 $238.68   6.350%   $253.8362   $253.84   $253.85   $253.80  
  Purchase #6 $228.34   3.189%   $235.6218   $235.62   $235.60   $235.60  
  Purchase #7 $102.48   6.204%   $108.8379   $108.84   $108.85   $108.80  
  7 purchase totals = $1,149.27       $1,217.4999   $1,217.51   $1,217.50   $1,217.40