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 $161.78   10.694%   $179.0808   $179.08   $179.10   $179.10  
  Purchase #2 $246.74   12.211%   $276.8694   $276.87   $276.85   $276.90  
  Purchase #3 $199.57   12.666%   $224.8475   $224.85   $224.85   $224.80  
  Purchase #4 $55.81   6.420%   $59.393   $59.39   $59.40   $59.40  
  Purchase #5 $146.65   10.365%   $161.8503   $161.85   $161.85   $161.90  
  Purchase #6 $136.41   8.132%   $147.5029   $147.50   $147.50   $147.50  
  Purchase #7 $67.43   5.433%   $71.0935   $71.09   $71.10   $71.10  
  7 purchase totals = $1,014.39       $1,120.6374   $1,120.63   $1,120.65   $1,120.70