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 $64.67   12.206%   $72.5636   $72.56   $72.55   $72.60  
  Purchase #2 $225.35   10.293%   $248.5453   $248.55   $248.55   $248.50  
  Purchase #3 $117.78   5.767%   $124.5724   $124.57   $124.55   $124.60  
  Purchase #4 $50.70   6.723%   $54.1086   $54.11   $54.10   $54.10  
  Purchase #5 $201.80   3.116%   $208.0881   $208.09   $208.10   $208.10  
  Purchase #6 $210.39   5.346%   $221.6374   $221.64   $221.65   $221.60  
  Purchase #7 $84.25   12.362%   $94.665   $94.67   $94.65   $94.70  
  7 purchase totals = $954.94       $1,024.1804   $1,024.19   $1,024.15   $1,024.20