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 $60.26   12.611%   $67.8594   $67.86   $67.85   $67.90  
  Purchase #2 $224.75   9.222%   $245.4764   $245.48   $245.50   $245.50  
  Purchase #3 $83.87   12.148%   $94.0585   $94.06   $94.05   $94.10  
  Purchase #4 $45.91   8.397%   $49.7651   $49.77   $49.75   $49.80  
  Purchase #5 $117.58   3.848%   $122.1045   $122.10   $122.10   $122.10  
  Purchase #6 $231.71   13.766%   $263.6072   $263.61   $263.60   $263.60  
  Purchase #7 $18.36   3.315%   $18.9686   $18.97   $18.95   $19.00  
  7 purchase totals = $782.44       $861.8397   $861.85   $861.80   $862.00