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 $232.56   5.756%   $245.9462   $245.95   $245.95   $245.90  
  Purchase #2 $235.27   9.380%   $257.3383   $257.34   $257.35   $257.30  
  Purchase #3 $61.41   11.858%   $68.692   $68.69   $68.70   $68.70  
  Purchase #4 $66.43   10.744%   $73.5672   $73.57   $73.55   $73.60  
  Purchase #5 $23.38   8.786%   $25.4342   $25.43   $25.45   $25.40  
  Purchase #6 $81.58   12.440%   $91.7286   $91.73   $91.75   $91.70  
  Purchase #7 $236.77   6.791%   $252.8491   $252.85   $252.85   $252.80  
  7 purchase totals = $937.40       $1,015.5556   $1,015.56   $1,015.60   $1,015.40