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 $69.93   9.514%   $76.5831   $76.58   $76.60   $76.60  
  Purchase #2 $100.92   11.791%   $112.8195   $112.82   $112.80   $112.80  
  Purchase #3 $192.77   12.521%   $216.9067   $216.91   $216.90   $216.90  
  Purchase #4 $195.34   5.679%   $206.4334   $206.43   $206.45   $206.40  
  Purchase #5 $32.51   7.718%   $35.0191   $35.02   $35.00   $35.00  
  Purchase #6 $99.48   12.258%   $111.6743   $111.67   $111.65   $111.70  
  Purchase #7 $106.72   3.277%   $110.2172   $110.22   $110.20   $110.20  
  7 purchase totals = $797.67       $869.6533   $869.65   $869.60   $869.60