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 $119.96   12.533%   $134.9946   $134.99   $135.00   $135.00  
  Purchase #2 $218.85   6.552%   $233.1891   $233.19   $233.20   $233.20  
  Purchase #3 $122.68   3.164%   $126.5616   $126.56   $126.55   $126.60  
  Purchase #4 $46.34   7.658%   $49.8887   $49.89   $49.90   $49.90  
  Purchase #5 $179.34   8.616%   $194.7919   $194.79   $194.80   $194.80  
  Purchase #6 $48.88   9.530%   $53.5383   $53.54   $53.55   $53.50  
  Purchase #7 $241.32   3.677%   $250.1933   $250.19   $250.20   $250.20  
  7 purchase totals = $977.37       $1,043.1575   $1,043.15   $1,043.20   $1,043.20