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 $76.56   12.803%   $86.362   $86.36   $86.35   $86.40  
  Purchase #2 $176.32   10.496%   $194.8265   $194.83   $194.85   $194.80  
  Purchase #3 $151.86   10.111%   $167.2146   $167.21   $167.20   $167.20  
  Purchase #4 $50.57   4.533%   $52.8623   $52.86   $52.85   $52.90  
  Purchase #5 $169.81   12.490%   $191.0193   $191.02   $191.00   $191.00  
  Purchase #6 $241.69   7.559%   $259.9593   $259.96   $259.95   $260.00  
  Purchase #7 $32.57   6.674%   $34.7437   $34.74   $34.75   $34.70  
  7 purchase totals = $899.38       $986.9877   $986.98   $986.95   $987.00