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 $239.56   12.562%   $269.6535   $269.65   $269.65   $269.70  
  Purchase #2 $30.91   4.152%   $32.1934   $32.19   $32.20   $32.20  
  Purchase #3 $29.49   11.419%   $32.8575   $32.86   $32.85   $32.90  
  Purchase #4 $183.88   12.190%   $206.295   $206.30   $206.30   $206.30  
  Purchase #5 $172.86   12.577%   $194.6006   $194.60   $194.60   $194.60  
  Purchase #6 $41.88   10.308%   $46.197   $46.20   $46.20   $46.20  
  Purchase #7 $148.30   4.326%   $154.7155   $154.72   $154.70   $154.70  
  7 purchase totals = $846.88       $936.5125   $936.52   $936.50   $936.60