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 $204.65   6.650%   $218.2592   $218.26   $218.25   $218.30  
  Purchase #2 $114.66   8.103%   $123.9509   $123.95   $123.95   $124.00  
  Purchase #3 $69.49   7.223%   $74.5093   $74.51   $74.50   $74.50  
  Purchase #4 $14.93   11.324%   $16.6207   $16.62   $16.60   $16.60  
  Purchase #5 $186.85   9.547%   $204.6886   $204.69   $204.70   $204.70  
  Purchase #6 $60.74   10.427%   $67.0734   $67.07   $67.05   $67.10  
  Purchase #7 $209.81   6.496%   $223.4393   $223.44   $223.45   $223.40  
  7 purchase totals = $861.13       $928.5414   $928.54   $928.50   $928.60