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 $67.28   9.662%   $73.7806   $73.78   $73.80   $73.80  
  Purchase #2 $70.55   6.838%   $75.3742   $75.37   $75.35   $75.40  
  Purchase #3 $16.83   13.496%   $19.1014   $19.10   $19.10   $19.10  
  Purchase #4 $208.89   11.366%   $232.6324   $232.63   $232.65   $232.60  
  Purchase #5 $238.85   10.364%   $263.6044   $263.60   $263.60   $263.60  
  Purchase #6 $210.83   13.457%   $239.2014   $239.20   $239.20   $239.20  
  Purchase #7 $98.34   4.757%   $103.018   $103.02   $103.00   $103.00  
  7 purchase totals = $911.57       $1,006.7124   $1,006.70   $1,006.70   $1,006.70