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 $93.81   3.177%   $96.7903   $96.79   $96.80   $96.80  
  Purchase #2 $83.51   9.439%   $91.3925   $91.39   $91.40   $91.40  
  Purchase #3 $234.26   9.129%   $255.6456   $255.65   $255.65   $255.60  
  Purchase #4 $56.45   9.865%   $62.0188   $62.02   $62.00   $62.00  
  Purchase #5 $176.50   6.556%   $188.0713   $188.07   $188.05   $188.10  
  Purchase #6 $145.36   6.434%   $154.7125   $154.71   $154.70   $154.70  
  Purchase #7 $47.82   5.481%   $50.441   $50.44   $50.45   $50.40  
  7 purchase totals = $837.71       $899.0720   $899.07   $899.05   $899.00