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 $96.66   13.713%   $109.915   $109.92   $109.90   $109.90  
  Purchase #2 $138.63   12.753%   $156.3095   $156.31   $156.30   $156.30  
  Purchase #3 $20.95   12.638%   $23.5977   $23.60   $23.60   $23.60  
  Purchase #4 $241.43   13.691%   $274.4842   $274.48   $274.50   $274.50  
  Purchase #5 $68.57   7.222%   $73.5221   $73.52   $73.50   $73.50  
  Purchase #6 $138.45   6.472%   $147.4105   $147.41   $147.40   $147.40  
  Purchase #7 $208.92   8.750%   $227.2005   $227.20   $227.20   $227.20  
  7 purchase totals = $913.61       $1,012.4395   $1,012.44   $1,012.40   $1,012.40