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 $67.77   12.677%   $76.3612   $76.36   $76.35   $76.40  
  Purchase #2 $17.33   6.610%   $18.4755   $18.48   $18.50   $18.50  
  Purchase #3 $198.36   5.173%   $208.6212   $208.62   $208.60   $208.60  
  Purchase #4 $153.37   9.491%   $167.9263   $167.93   $167.95   $167.90  
  Purchase #5 $61.84   10.767%   $68.4983   $68.50   $68.50   $68.50  
  Purchase #6 $246.68   11.112%   $274.0911   $274.09   $274.10   $274.10  
  Purchase #7 $202.48   9.478%   $221.6711   $221.67   $221.65   $221.70  
  7 purchase totals = $947.83       $1,035.6447   $1,035.65   $1,035.65   $1,035.70