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 $227.38   7.173%   $243.69   $243.69   $243.70   $243.70  
  Purchase #2 $68.94   12.473%   $77.5389   $77.54   $77.55   $77.50  
  Purchase #3 $182.55   12.758%   $205.8397   $205.84   $205.85   $205.80  
  Purchase #4 $201.60   8.439%   $218.613   $218.61   $218.60   $218.60  
  Purchase #5 $67.61   8.869%   $73.6063   $73.61   $73.60   $73.60  
  Purchase #6 $12.71   3.627%   $13.171   $13.17   $13.15   $13.20  
  Purchase #7 $234.45   8.852%   $255.2035   $255.20   $255.20   $255.20  
  7 purchase totals = $995.24       $1,087.6624   $1,087.66   $1,087.65   $1,087.60