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 $76.96   9.364%   $84.1665   $84.17   $84.15   $84.20  
  Purchase #2 $111.71   11.835%   $124.9309   $124.93   $124.95   $124.90  
  Purchase #3 $192.56   8.152%   $208.2575   $208.26   $208.25   $208.30  
  Purchase #4 $129.92   4.513%   $135.7833   $135.78   $135.80   $135.80  
  Purchase #5 $210.67   13.171%   $238.4173   $238.42   $238.40   $238.40  
  Purchase #6 $58.82   12.458%   $66.1478   $66.15   $66.15   $66.10  
  Purchase #7 $183.55   7.144%   $196.6628   $196.66   $196.65   $196.70  
  7 purchase totals = $964.19       $1,054.3661   $1,054.37   $1,054.35   $1,054.40