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 $65.58   12.102%   $73.5165   $73.52   $73.50   $73.50  
  Purchase #2 $190.40   3.763%   $197.5648   $197.56   $197.55   $197.60  
  Purchase #3 $67.89   7.582%   $73.0374   $73.04   $73.05   $73.00  
  Purchase #4 $236.70   5.402%   $249.4865   $249.49   $249.50   $249.50  
  Purchase #5 $54.86   9.372%   $60.0015   $60.00   $60.00   $60.00  
  Purchase #6 $132.34   6.659%   $141.1525   $141.15   $141.15   $141.20  
  Purchase #7 $48.67   8.697%   $52.9028   $52.90   $52.90   $52.90  
  7 purchase totals = $796.44       $847.6620   $847.66   $847.65   $847.70