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 $58.64   4.534%   $61.2987   $61.30   $61.30   $61.30  
  Purchase #2 $80.60   7.542%   $86.6789   $86.68   $86.70   $86.70  
  Purchase #3 $17.41   10.502%   $19.2384   $19.24   $19.25   $19.20  
  Purchase #4 $170.77   11.465%   $190.3488   $190.35   $190.35   $190.30  
  Purchase #5 $210.53   10.724%   $233.1072   $233.11   $233.10   $233.10  
  Purchase #6 $154.85   10.632%   $171.3137   $171.31   $171.30   $171.30  
  Purchase #7 $16.87   7.866%   $18.197   $18.20   $18.20   $18.20  
  7 purchase totals = $709.67       $780.1827   $780.19   $780.20   $780.10