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 $237.51   10.612%   $262.7146   $262.71   $262.70   $262.70  
  Purchase #2 $225.25   4.275%   $234.8794   $234.88   $234.90   $234.90  
  Purchase #3 $200.30   5.439%   $211.1943   $211.19   $211.20   $211.20  
  Purchase #4 $249.52   12.587%   $280.9271   $280.93   $280.95   $280.90  
  Purchase #5 $15.77   6.822%   $16.8458   $16.85   $16.85   $16.80  
  Purchase #6 $221.75   9.602%   $243.0424   $243.04   $243.05   $243.00  
  Purchase #7 $11.61   10.710%   $12.8534   $12.85   $12.85   $12.90  
  7 purchase totals = $1,161.71       $1,262.4570   $1,262.45   $1,262.50   $1,262.40