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 $57.74   8.397%   $62.5884   $62.59   $62.60   $62.60  
  Purchase #2 $247.47   11.251%   $275.3128   $275.31   $275.30   $275.30  
  Purchase #3 $245.35   7.279%   $263.209   $263.21   $263.20   $263.20  
  Purchase #4 $45.76   7.514%   $49.1984   $49.20   $49.20   $49.20  
  Purchase #5 $143.25   4.393%   $149.543   $149.54   $149.55   $149.50  
  Purchase #6 $162.66   3.397%   $168.1856   $168.19   $168.20   $168.20  
  Purchase #7 $245.27   13.689%   $278.845   $278.85   $278.85   $278.80  
  7 purchase totals = $1,147.50       $1,246.8822   $1,246.89   $1,246.90   $1,246.80