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 $85.35   11.293%   $94.9886   $94.99   $95.00   $95.00  
  Purchase #2 $133.57   9.305%   $145.9987   $146.00   $146.00   $146.00  
  Purchase #3 $157.72   4.451%   $164.7401   $164.74   $164.75   $164.70  
  Purchase #4 $130.74   5.131%   $137.4483   $137.45   $137.45   $137.40  
  Purchase #5 $117.52   4.570%   $122.8907   $122.89   $122.90   $122.90  
  Purchase #6 $243.91   5.389%   $257.0543   $257.05   $257.05   $257.10  
  Purchase #7 $72.62   12.227%   $81.4992   $81.50   $81.50   $81.50  
  7 purchase totals = $941.43       $1,004.6199   $1,004.62   $1,004.65   $1,004.60