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 $54.81   9.511%   $60.023   $60.02   $60.00   $60.00  
  Purchase #2 $179.68   4.493%   $187.753   $187.75   $187.75   $187.80  
  Purchase #3 $51.69   4.371%   $53.9494   $53.95   $53.95   $53.90  
  Purchase #4 $238.50   3.207%   $246.1487   $246.15   $246.15   $246.10  
  Purchase #5 $114.77   13.206%   $129.9265   $129.93   $129.95   $129.90  
  Purchase #6 $34.78   9.274%   $38.0055   $38.01   $38.00   $38.00  
  Purchase #7 $81.64   9.717%   $89.573   $89.57   $89.55   $89.60  
  7 purchase totals = $755.87       $805.3791   $805.38   $805.35   $805.30