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 $189.41   6.260%   $201.2671   $201.27   $201.25   $201.30  
  Purchase #2 $151.69   7.463%   $163.0106   $163.01   $163.00   $163.00  
  Purchase #3 $109.44   13.213%   $123.9003   $123.90   $123.90   $123.90  
  Purchase #4 $158.64   3.748%   $164.5858   $164.59   $164.60   $164.60  
  Purchase #5 $136.62   8.351%   $148.0291   $148.03   $148.05   $148.00  
  Purchase #6 $121.28   11.551%   $135.2891   $135.29   $135.30   $135.30  
  Purchase #7 $80.80   4.849%   $84.718   $84.72   $84.70   $84.70  
  7 purchase totals = $947.88       $1,020.8000   $1,020.81   $1,020.80   $1,020.80