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 $205.55   8.705%   $223.4431   $223.44   $223.45   $223.40  
  Purchase #2 $22.64   9.783%   $24.8549   $24.85   $24.85   $24.90  
  Purchase #3 $193.70   13.670%   $220.1788   $220.18   $220.20   $220.20  
  Purchase #4 $44.63   4.288%   $46.5437   $46.54   $46.55   $46.50  
  Purchase #5 $70.33   13.694%   $79.961   $79.96   $79.95   $80.00  
  Purchase #6 $187.27   6.187%   $198.8564   $198.86   $198.85   $198.90  
  Purchase #7 $237.36   13.617%   $269.6813   $269.68   $269.70   $269.70  
  7 purchase totals = $961.48       $1,063.5192   $1,063.51   $1,063.55   $1,063.60