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 $241.57   3.605%   $250.2786   $250.28   $250.30   $250.30  
  Purchase #2 $89.88   5.644%   $94.9528   $94.95   $94.95   $95.00  
  Purchase #3 $136.36   10.390%   $150.5278   $150.53   $150.55   $150.50  
  Purchase #4 $220.70   8.333%   $239.0909   $239.09   $239.10   $239.10  
  Purchase #5 $175.41   12.618%   $197.5432   $197.54   $197.55   $197.50  
  Purchase #6 $206.98   13.715%   $235.3673   $235.37   $235.35   $235.40  
  Purchase #7 $54.36   10.458%   $60.045   $60.05   $60.05   $60.00  
  7 purchase totals = $1,125.26       $1,227.8056   $1,227.81   $1,227.85   $1,227.80