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 $68.88   11.544%   $76.8315   $76.83   $76.85   $76.80  
  Purchase #2 $157.60   10.106%   $173.5271   $173.53   $173.55   $173.50  
  Purchase #3 $22.91   12.345%   $25.7382   $25.74   $25.75   $25.70  
  Purchase #4 $57.31   10.706%   $63.4456   $63.45   $63.45   $63.40  
  Purchase #5 $183.30   8.488%   $198.8585   $198.86   $198.85   $198.90  
  Purchase #6 $30.96   6.362%   $32.9297   $32.93   $32.95   $32.90  
  Purchase #7 $83.78   5.339%   $88.253   $88.25   $88.25   $88.30  
  7 purchase totals = $604.74       $659.5836   $659.59   $659.65   $659.50