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 $92.56   12.109%   $103.7681   $103.77   $103.75   $103.80  
  Purchase #2 $247.72   11.237%   $275.5563   $275.56   $275.55   $275.60  
  Purchase #3 $43.42   7.847%   $46.8272   $46.83   $46.85   $46.80  
  Purchase #4 $183.57   5.166%   $193.0532   $193.05   $193.05   $193.10  
  Purchase #5 $88.73   7.846%   $95.6918   $95.69   $95.70   $95.70  
  Purchase #6 $27.69   5.116%   $29.1066   $29.11   $29.10   $29.10  
  Purchase #7 $249.44   11.227%   $277.4446   $277.44   $277.45   $277.40  
  7 purchase totals = $933.13       $1,021.4478   $1,021.45   $1,021.45   $1,021.50