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 $60.94   8.391%   $66.0535   $66.05   $66.05   $66.10  
  Purchase #2 $225.51   13.356%   $255.6291   $255.63   $255.65   $255.60  
  Purchase #3 $7.57   6.111%   $8.0326   $8.03   $8.05   $8.00  
  Purchase #4 $245.62   13.461%   $278.6829   $278.68   $278.70   $278.70  
  Purchase #5 $19.90   8.247%   $21.5412   $21.54   $21.55   $21.50  
  Purchase #6 $169.45   8.579%   $183.9871   $183.99   $184.00   $184.00  
  Purchase #7 $224.71   6.345%   $238.9678   $238.97   $238.95   $239.00  
  7 purchase totals = $953.70       $1,052.8942   $1,052.89   $1,052.95   $1,052.90