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 $59.37   8.807%   $64.5987   $64.60   $64.60   $64.60  
  Purchase #2 $40.79   6.151%   $43.299   $43.30   $43.30   $43.30  
  Purchase #3 $109.96   3.629%   $113.9504   $113.95   $113.95   $114.00  
  Purchase #4 $23.64   6.550%   $25.1884   $25.19   $25.20   $25.20  
  Purchase #5 $145.45   6.451%   $154.833   $154.83   $154.85   $154.80  
  Purchase #6 $246.97   12.532%   $277.9203   $277.92   $277.90   $277.90  
  Purchase #7 $238.86   4.481%   $249.5633   $249.56   $249.55   $249.60  
  7 purchase totals = $865.04       $929.3531   $929.35   $929.35   $929.40