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 $92.84   5.717%   $98.1477   $98.15   $98.15   $98.10  
  Purchase #2 $76.82   13.679%   $87.3282   $87.33   $87.35   $87.30  
  Purchase #3 $225.37   11.238%   $250.6971   $250.70   $250.70   $250.70  
  Purchase #4 $86.90   13.826%   $98.9148   $98.91   $98.90   $98.90  
  Purchase #5 $141.44   8.118%   $152.9221   $152.92   $152.90   $152.90  
  Purchase #6 $11.46   5.686%   $12.1116   $12.11   $12.10   $12.10  
  Purchase #7 $155.89   3.806%   $161.8232   $161.82   $161.80   $161.80  
  7 purchase totals = $790.72       $861.9447   $861.94   $861.90   $861.80