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 $85.36   12.786%   $96.2741   $96.27   $96.25   $96.30  
  Purchase #2 $134.37   9.265%   $146.8194   $146.82   $146.80   $146.80  
  Purchase #3 $237.66   10.274%   $262.0772   $262.08   $262.10   $262.10  
  Purchase #4 $28.93   7.114%   $30.9881   $30.99   $31.00   $31.00  
  Purchase #5 $244.87   9.603%   $268.3849   $268.38   $268.40   $268.40  
  Purchase #6 $170.58   5.143%   $179.3529   $179.35   $179.35   $179.40  
  Purchase #7 $230.60   7.636%   $248.2086   $248.21   $248.20   $248.20  
  7 purchase totals = $1,132.37       $1,232.1052   $1,232.10   $1,232.10   $1,232.20