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 $228.84   8.487%   $248.2617   $248.26   $248.25   $248.30  
  Purchase #2 $59.70   8.727%   $64.91   $64.91   $64.90   $64.90  
  Purchase #3 $48.25   5.369%   $50.8405   $50.84   $50.85   $50.80  
  Purchase #4 $212.94   10.313%   $234.9005   $234.90   $234.90   $234.90  
  Purchase #5 $102.31   6.539%   $109.0001   $109.00   $109.00   $109.00  
  Purchase #6 $42.98   9.421%   $47.0291   $47.03   $47.05   $47.00  
  Purchase #7 $27.70   10.797%   $30.6908   $30.69   $30.70   $30.70  
  7 purchase totals = $722.72       $785.6327   $785.63   $785.65   $785.60