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 $176.62   9.128%   $192.7419   $192.74   $192.75   $192.70  
  Purchase #2 $49.83   4.171%   $51.9084   $51.91   $51.90   $51.90  
  Purchase #3 $35.62   12.296%   $39.9998   $40.00   $40.00   $40.00  
  Purchase #4 $213.29   3.818%   $221.4334   $221.43   $221.45   $221.40  
  Purchase #5 $198.62   9.785%   $218.055   $218.06   $218.05   $218.10  
  Purchase #6 $167.44   13.263%   $189.6476   $189.65   $189.65   $189.60  
  Purchase #7 $76.81   6.295%   $81.6452   $81.65   $81.65   $81.60  
  7 purchase totals = $918.23       $995.4313   $995.44   $995.45   $995.30