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 $176.59   12.837%   $199.2589   $199.26   $199.25   $199.30  
  Purchase #2 $233.55   8.246%   $252.8085   $252.81   $252.80   $252.80  
  Purchase #3 $116.58   8.745%   $126.7749   $126.77   $126.75   $126.80  
  Purchase #4 $127.55   3.338%   $131.8076   $131.81   $131.80   $131.80  
  Purchase #5 $39.45   9.861%   $43.3402   $43.34   $43.35   $43.30  
  Purchase #6 $225.93   6.706%   $241.0809   $241.08   $241.10   $241.10  
  Purchase #7 $232.29   10.867%   $257.533   $257.53   $257.55   $257.50  
  7 purchase totals = $1,151.94       $1,252.6040   $1,252.60   $1,252.60   $1,252.60