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 $182.43   12.536%   $205.2994   $205.30   $205.30   $205.30  
  Purchase #2 $91.72   4.138%   $95.5154   $95.52   $95.50   $95.50  
  Purchase #3 $80.72   6.606%   $86.0524   $86.05   $86.05   $86.10  
  Purchase #4 $10.49   7.316%   $11.2574   $11.26   $11.25   $11.30  
  Purchase #5 $38.83   5.148%   $40.829   $40.83   $40.85   $40.80  
  Purchase #6 $97.89   12.522%   $110.1478   $110.15   $110.15   $110.10  
  Purchase #7 $60.84   11.757%   $67.993   $67.99   $68.00   $68.00  
  7 purchase totals = $562.92       $617.0944   $617.10   $617.10   $617.10