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 $48.86   5.393%   $51.495   $51.50   $51.50   $51.50  
  Purchase #2 $198.86   6.572%   $211.9291   $211.93   $211.95   $211.90  
  Purchase #3 $245.96   13.433%   $278.9998   $279.00   $279.00   $279.00  
  Purchase #4 $52.30   7.233%   $56.0829   $56.08   $56.10   $56.10  
  Purchase #5 $180.37   5.228%   $189.7997   $189.80   $189.80   $189.80  
  Purchase #6 $244.35   7.222%   $261.997   $262.00   $262.00   $262.00  
  Purchase #7 $146.97   11.423%   $163.7584   $163.76   $163.75   $163.80  
  7 purchase totals = $1,117.67       $1,214.0619   $1,214.07   $1,214.10   $1,214.10