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 $93.61   3.357%   $96.7525   $96.75   $96.75   $96.80  
  Purchase #2 $249.34   10.655%   $275.9072   $275.91   $275.90   $275.90  
  Purchase #3 $153.58   9.352%   $167.9428   $167.94   $167.95   $167.90  
  Purchase #4 $81.79   8.798%   $88.9859   $88.99   $89.00   $89.00  
  Purchase #5 $16.85   5.826%   $17.8317   $17.83   $17.85   $17.80  
  Purchase #6 $229.94   12.332%   $258.2962   $258.30   $258.30   $258.30  
  Purchase #7 $194.43   7.453%   $208.9209   $208.92   $208.90   $208.90  
  7 purchase totals = $1,019.54       $1,114.6372   $1,114.64   $1,114.65   $1,114.60