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 $64.86   6.791%   $69.2646   $69.26   $69.25   $69.30  
  Purchase #2 $6.33   7.513%   $6.8056   $6.81   $6.80   $6.80  
  Purchase #3 $121.63   3.632%   $126.0476   $126.05   $126.05   $126.00  
  Purchase #4 $17.75   11.260%   $19.7487   $19.75   $19.75   $19.70  
  Purchase #5 $70.86   9.461%   $77.5641   $77.56   $77.55   $77.60  
  Purchase #6 $178.25   13.430%   $202.189   $202.19   $202.20   $202.20  
  Purchase #7 $118.58   5.378%   $124.9572   $124.96   $124.95   $125.00  
  7 purchase totals = $578.26       $626.5768   $626.58   $626.55   $626.60