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 $22.97   10.580%   $25.4002   $25.40   $25.40   $25.40  
  Purchase #2 $117.30   8.564%   $127.3456   $127.35   $127.35   $127.30  
  Purchase #3 $69.34   8.745%   $75.4038   $75.40   $75.40   $75.40  
  Purchase #4 $202.74   4.188%   $211.2308   $211.23   $211.25   $211.20  
  Purchase #5 $143.72   6.763%   $153.4398   $153.44   $153.45   $153.40  
  Purchase #6 $222.83   8.460%   $241.6814   $241.68   $241.70   $241.70  
  Purchase #7 $242.72   10.172%   $267.4095   $267.41   $267.40   $267.40  
  7 purchase totals = $1,021.62       $1,101.9111   $1,101.91   $1,101.95   $1,101.80