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 $207.25   8.395%   $224.6486   $224.65   $224.65   $224.60  
  Purchase #2 $129.63   10.487%   $143.2243   $143.22   $143.20   $143.20  
  Purchase #3 $52.95   5.659%   $55.9464   $55.95   $55.95   $55.90  
  Purchase #4 $115.55   11.513%   $128.8533   $128.85   $128.85   $128.90  
  Purchase #5 $191.69   8.259%   $207.5217   $207.52   $207.50   $207.50  
  Purchase #6 $141.64   3.727%   $146.9189   $146.92   $146.90   $146.90  
  Purchase #7 $106.91   4.349%   $111.5595   $111.56   $111.55   $111.60  
  7 purchase totals = $945.62       $1,018.6727   $1,018.67   $1,018.60   $1,018.60