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 $56.80   11.140%   $63.1275   $63.13   $63.15   $63.10  
  Purchase #2 $88.48   8.458%   $95.9636   $95.96   $95.95   $96.00  
  Purchase #3 $248.66   8.729%   $270.3655   $270.37   $270.35   $270.40  
  Purchase #4 $64.58   4.787%   $67.6714   $67.67   $67.65   $67.70  
  Purchase #5 $38.44   3.862%   $39.9246   $39.92   $39.90   $39.90  
  Purchase #6 $136.47   13.479%   $154.8648   $154.86   $154.85   $154.90  
  Purchase #7 $74.90   10.440%   $82.7196   $82.72   $82.70   $82.70  
  7 purchase totals = $708.33       $774.6370   $774.63   $774.55   $774.70