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 $233.58   8.670%   $253.8314   $253.83   $253.85   $253.80  
  Purchase #2 $138.84   10.163%   $152.9503   $152.95   $152.95   $153.00  
  Purchase #3 $23.82   6.730%   $25.4231   $25.42   $25.40   $25.40  
  Purchase #4 $189.31   13.817%   $215.467   $215.47   $215.45   $215.50  
  Purchase #5 $119.81   10.304%   $132.1552   $132.16   $132.15   $132.20  
  Purchase #6 $64.26   10.463%   $70.9835   $70.98   $71.00   $71.00  
  Purchase #7 $248.43   13.668%   $282.3854   $282.39   $282.40   $282.40  
  7 purchase totals = $1,018.05       $1,133.1959   $1,133.20   $1,133.20   $1,133.30