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 $185.43   12.166%   $207.9894   $207.99   $208.00   $208.00  
  Purchase #2 $152.46   4.321%   $159.0478   $159.05   $159.05   $159.00  
  Purchase #3 $169.62   13.669%   $192.8054   $192.81   $192.80   $192.80  
  Purchase #4 $126.81   3.141%   $130.7931   $130.79   $130.80   $130.80  
  Purchase #5 $211.36   7.773%   $227.789   $227.79   $227.80   $227.80  
  Purchase #6 $224.46   9.647%   $246.1137   $246.11   $246.10   $246.10  
  Purchase #7 $194.84   9.319%   $212.9971   $213.00   $213.00   $213.00  
  7 purchase totals = $1,264.98       $1,377.5355   $1,377.54   $1,377.55   $1,377.50