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 $208.46   11.695%   $232.8394   $232.84   $232.85   $232.80  
  Purchase #2 $111.41   12.742%   $125.6059   $125.61   $125.60   $125.60  
  Purchase #3 $63.44   6.253%   $67.4069   $67.41   $67.40   $67.40  
  Purchase #4 $30.47   5.479%   $32.1395   $32.14   $32.15   $32.10  
  Purchase #5 $23.63   6.217%   $25.0991   $25.10   $25.10   $25.10  
  Purchase #6 $111.97   10.173%   $123.3607   $123.36   $123.35   $123.40  
  Purchase #7 $142.73   6.856%   $152.5156   $152.52   $152.50   $152.50  
  7 purchase totals = $692.11       $758.9671   $758.98   $758.95   $758.90