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 $182.83   8.242%   $197.8988   $197.90   $197.90   $197.90  
  Purchase #2 $116.31   6.566%   $123.9469   $123.95   $123.95   $123.90  
  Purchase #3 $232.28   9.239%   $253.7403   $253.74   $253.75   $253.70  
  Purchase #4 $243.78   9.444%   $266.8026   $266.80   $266.80   $266.80  
  Purchase #5 $28.95   11.703%   $32.338   $32.34   $32.35   $32.30  
  Purchase #6 $162.58   5.753%   $171.9332   $171.93   $171.95   $171.90  
  Purchase #7 $127.62   10.630%   $141.186   $141.19   $141.20   $141.20  
  7 purchase totals = $1,094.35       $1,187.8458   $1,187.85   $1,187.90   $1,187.70