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 $173.84   13.656%   $197.5796   $197.58   $197.60   $197.60  
  Purchase #2 $151.99   13.463%   $172.4524   $172.45   $172.45   $172.50  
  Purchase #3 $30.25   12.613%   $34.0654   $34.07   $34.05   $34.10  
  Purchase #4 $213.40   13.365%   $241.9209   $241.92   $241.90   $241.90  
  Purchase #5 $235.45   3.491%   $243.6696   $243.67   $243.65   $243.70  
  Purchase #6 $148.82   12.144%   $166.8927   $166.89   $166.90   $166.90  
  Purchase #7 $187.49   8.601%   $203.616   $203.62   $203.60   $203.60  
  7 purchase totals = $1,141.24       $1,260.1966   $1,260.20   $1,260.15   $1,260.30