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 $56.95   11.610%   $63.5619   $63.56   $63.55   $63.60  
  Purchase #2 $22.91   10.758%   $25.3747   $25.37   $25.35   $25.40  
  Purchase #3 $116.28   7.650%   $125.1754   $125.18   $125.20   $125.20  
  Purchase #4 $220.62   8.366%   $239.0771   $239.08   $239.10   $239.10  
  Purchase #5 $250.80   12.705%   $282.6641   $282.66   $282.65   $282.70  
  Purchase #6 $146.44   7.269%   $157.0847   $157.08   $157.10   $157.10  
  Purchase #7 $100.31   8.608%   $108.9447   $108.94   $108.95   $108.90  
  7 purchase totals = $914.31       $1,001.8826   $1,001.87   $1,001.90   $1,002.00