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 $13.48   8.482%   $14.6234   $14.62   $14.60   $14.60  
  Purchase #2 $235.59   13.449%   $267.2745   $267.27   $267.25   $267.30  
  Purchase #3 $189.43   6.609%   $201.9494   $201.95   $201.95   $201.90  
  Purchase #4 $249.28   3.461%   $257.9076   $257.91   $257.90   $257.90  
  Purchase #5 $135.67   4.222%   $141.398   $141.40   $141.40   $141.40  
  Purchase #6 $96.39   4.178%   $100.4172   $100.42   $100.40   $100.40  
  Purchase #7 $243.61   11.503%   $271.6325   $271.63   $271.65   $271.60  
  7 purchase totals = $1,163.45       $1,255.2026   $1,255.20   $1,255.15   $1,255.10