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 $151.85   6.703%   $162.0285   $162.03   $162.05   $162.00  
  Purchase #2 $173.43   13.612%   $197.0373   $197.04   $197.05   $197.00  
  Purchase #3 $166.72   3.114%   $171.9117   $171.91   $171.90   $171.90  
  Purchase #4 $133.33   10.771%   $147.691   $147.69   $147.70   $147.70  
  Purchase #5 $30.25   3.809%   $31.4022   $31.40   $31.40   $31.40  
  Purchase #6 $19.44   4.657%   $20.3453   $20.35   $20.35   $20.30  
  Purchase #7 $248.25   13.438%   $281.6098   $281.61   $281.60   $281.60  
  7 purchase totals = $923.27       $1,012.0258   $1,012.03   $1,012.05   $1,011.90