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 $242.87   4.171%   $253.0001   $253.00   $253.00   $253.00  
  Purchase #2 $176.33   8.772%   $191.7977   $191.80   $191.80   $191.80  
  Purchase #3 $75.59   6.340%   $80.3824   $80.38   $80.40   $80.40  
  Purchase #4 $164.81   5.212%   $173.3999   $173.40   $173.40   $173.40  
  Purchase #5 $59.75   6.313%   $63.522   $63.52   $63.50   $63.50  
  Purchase #6 $195.43   10.503%   $215.956   $215.96   $215.95   $216.00  
  Purchase #7 $33.67   6.746%   $35.9414   $35.94   $35.95   $35.90  
  7 purchase totals = $948.45       $1,013.9995   $1,014.00   $1,014.00   $1,014.00