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 $190.87   6.846%   $203.937   $203.94   $203.95   $203.90  
  Purchase #2 $233.48   11.598%   $260.559   $260.56   $260.55   $260.60  
  Purchase #3 $39.27   13.416%   $44.5385   $44.54   $44.55   $44.50  
  Purchase #4 $206.57   13.225%   $233.8889   $233.89   $233.90   $233.90  
  Purchase #5 $167.28   4.120%   $174.1719   $174.17   $174.15   $174.20  
  Purchase #6 $195.47   4.295%   $203.8654   $203.87   $203.85   $203.90  
  Purchase #7 $69.87   13.565%   $79.3479   $79.35   $79.35   $79.30  
  7 purchase totals = $1,102.81       $1,200.3086   $1,200.32   $1,200.30   $1,200.30