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 $138.53   12.402%   $155.7105   $155.71   $155.70   $155.70  
  Purchase #2 $45.25   10.288%   $49.9053   $49.91   $49.90   $49.90  
  Purchase #3 $233.43   12.506%   $262.6228   $262.62   $262.60   $262.60  
  Purchase #4 $81.59   5.512%   $86.0872   $86.09   $86.10   $86.10  
  Purchase #5 $5.68   7.582%   $6.1107   $6.11   $6.10   $6.10  
  Purchase #6 $108.48   9.652%   $118.9505   $118.95   $118.95   $119.00  
  Purchase #7 $163.90   11.654%   $183.0009   $183.00   $183.00   $183.00  
  7 purchase totals = $776.86       $862.3879   $862.39   $862.35   $862.40