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 $241.97   11.190%   $269.0464   $269.05   $269.05   $269.00  
  Purchase #2 $161.49   11.709%   $180.3989   $180.40   $180.40   $180.40  
  Purchase #3 $168.39   12.258%   $189.0312   $189.03   $189.05   $189.00  
  Purchase #4 $26.74   11.570%   $29.8338   $29.83   $29.85   $29.80  
  Purchase #5 $159.72   6.639%   $170.3238   $170.32   $170.30   $170.30  
  Purchase #6 $32.87   8.814%   $35.7672   $35.77   $35.75   $35.80  
  Purchase #7 $54.97   5.514%   $58.001   $58.00   $58.00   $58.00  
  7 purchase totals = $846.15       $932.4023   $932.40   $932.40   $932.30