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 $246.96   8.581%   $268.1516   $268.15   $268.15   $268.20  
  Purchase #2 $241.96   3.602%   $250.6754   $250.68   $250.70   $250.70  
  Purchase #3 $58.92   12.608%   $66.3486   $66.35   $66.35   $66.30  
  Purchase #4 $115.42   8.807%   $125.585   $125.59   $125.60   $125.60  
  Purchase #5 $38.29   6.414%   $40.7459   $40.75   $40.75   $40.70  
  Purchase #6 $240.84   6.787%   $257.1858   $257.19   $257.20   $257.20  
  Purchase #7 $63.41   6.487%   $67.5234   $67.52   $67.50   $67.50  
  7 purchase totals = $1,005.80       $1,076.2157   $1,076.23   $1,076.25   $1,076.20