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 $42.65   10.267%   $47.0289   $47.03   $47.05   $47.00  
  Purchase #2 $200.50   9.392%   $219.331   $219.33   $219.35   $219.30  
  Purchase #3 $73.53   4.174%   $76.5991   $76.60   $76.60   $76.60  
  Purchase #4 $237.40   8.217%   $256.9072   $256.91   $256.90   $256.90  
  Purchase #5 $27.32   13.342%   $30.965   $30.97   $30.95   $31.00  
  Purchase #6 $198.82   7.279%   $213.2921   $213.29   $213.30   $213.30  
  Purchase #7 $166.89   3.121%   $172.0986   $172.10   $172.10   $172.10  
  7 purchase totals = $947.11       $1,016.2219   $1,016.23   $1,016.25   $1,016.20