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 $31.66   12.315%   $35.5589   $35.56   $35.55   $35.60  
  Purchase #2 $167.85   6.635%   $178.9868   $178.99   $179.00   $179.00  
  Purchase #3 $14.93   11.809%   $16.6931   $16.69   $16.70   $16.70  
  Purchase #4 $134.61   12.319%   $151.1926   $151.19   $151.20   $151.20  
  Purchase #5 $161.57   6.106%   $171.4355   $171.44   $171.45   $171.40  
  Purchase #6 $207.75   5.418%   $219.0059   $219.01   $219.00   $219.00  
  Purchase #7 $195.30   6.813%   $208.6058   $208.61   $208.60   $208.60  
  7 purchase totals = $913.67       $981.4786   $981.49   $981.50   $981.50