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 $85.49   8.701%   $92.9285   $92.93   $92.95   $92.90  
  Purchase #2 $186.75   11.302%   $207.8565   $207.86   $207.85   $207.90  
  Purchase #3 $79.77   5.252%   $83.9595   $83.96   $83.95   $84.00  
  Purchase #4 $227.93   5.621%   $240.7419   $240.74   $240.75   $240.70  
  Purchase #5 $18.25   11.823%   $20.4077   $20.41   $20.40   $20.40  
  Purchase #6 $237.50   6.202%   $252.2298   $252.23   $252.25   $252.20  
  Purchase #7 $232.32   4.646%   $243.1136   $243.11   $243.10   $243.10  
  7 purchase totals = $1,068.01       $1,141.2375   $1,141.24   $1,141.25   $1,141.20