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 $176.54   6.356%   $187.7609   $187.76   $187.75   $187.80  
  Purchase #2 $59.83   11.155%   $66.504   $66.50   $66.50   $66.50  
  Purchase #3 $106.44   13.587%   $120.902   $120.90   $120.90   $120.90  
  Purchase #4 $77.60   6.559%   $82.6898   $82.69   $82.70   $82.70  
  Purchase #5 $236.57   7.330%   $253.9106   $253.91   $253.90   $253.90  
  Purchase #6 $211.58   6.313%   $224.937   $224.94   $224.95   $224.90  
  Purchase #7 $230.68   11.627%   $257.5012   $257.50   $257.50   $257.50  
  7 purchase totals = $1,099.24       $1,194.2055   $1,194.20   $1,194.20   $1,194.20