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 $151.51   6.495%   $161.3506   $161.35   $161.35   $161.40  
  Purchase #2 $141.88   4.254%   $147.9156   $147.92   $147.90   $147.90  
  Purchase #3 $231.85   11.731%   $259.0483   $259.05   $259.05   $259.00  
  Purchase #4 $106.94   8.707%   $116.2513   $116.25   $116.25   $116.30  
  Purchase #5 $174.27   13.448%   $197.7058   $197.71   $197.70   $197.70  
  Purchase #6 $5.85   12.873%   $6.6031   $6.60   $6.60   $6.60  
  Purchase #7 $135.61   6.397%   $144.285   $144.29   $144.30   $144.30  
  7 purchase totals = $947.91       $1,033.1597   $1,033.17   $1,033.15   $1,033.20