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 $54.26   12.352%   $60.9622   $60.96   $60.95   $61.00  
  Purchase #2 $8.77   3.830%   $9.1059   $9.11   $9.10   $9.10  
  Purchase #3 $68.63   5.573%   $72.4547   $72.45   $72.45   $72.50  
  Purchase #4 $78.68   8.251%   $85.1719   $85.17   $85.15   $85.20  
  Purchase #5 $106.25   11.327%   $118.2849   $118.28   $118.30   $118.30  
  Purchase #6 $209.87   4.626%   $219.5786   $219.58   $219.60   $219.60  
  Purchase #7 $34.74   10.379%   $38.3457   $38.35   $38.35   $38.30  
  7 purchase totals = $561.20       $603.9039   $603.90   $603.90   $604.00