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 $248.51   7.811%   $267.9211   $267.92   $267.90   $267.90  
  Purchase #2 $68.50   7.503%   $73.6396   $73.64   $73.65   $73.60  
  Purchase #3 $188.40   8.321%   $204.0768   $204.08   $204.10   $204.10  
  Purchase #4 $223.74   5.476%   $235.992   $235.99   $236.00   $236.00  
  Purchase #5 $69.54   9.324%   $76.0239   $76.02   $76.00   $76.00  
  Purchase #6 $199.37   9.631%   $218.5713   $218.57   $218.55   $218.60  
  Purchase #7 $87.32   12.314%   $98.0726   $98.07   $98.05   $98.10  
  7 purchase totals = $1,085.38       $1,174.2973   $1,174.29   $1,174.25   $1,174.30