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 $246.37   8.781%   $268.0037   $268.00   $268.00   $268.00  
  Purchase #2 $112.62   3.222%   $116.2486   $116.25   $116.25   $116.20  
  Purchase #3 $129.59   9.454%   $141.8414   $141.84   $141.85   $141.80  
  Purchase #4 $80.56   7.423%   $86.54   $86.54   $86.55   $86.50  
  Purchase #5 $241.90   11.139%   $268.8452   $268.85   $268.85   $268.80  
  Purchase #6 $182.36   8.863%   $198.5226   $198.52   $198.50   $198.50  
  Purchase #7 $163.97   5.355%   $172.7506   $172.75   $172.75   $172.80  
  7 purchase totals = $1,157.37       $1,252.7521   $1,252.75   $1,252.75   $1,252.60