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 $43.26   12.845%   $48.8167   $48.82   $48.80   $48.80  
  Purchase #2 $219.53   6.237%   $233.2221   $233.22   $233.20   $233.20  
  Purchase #3 $107.45   9.363%   $117.5105   $117.51   $117.50   $117.50  
  Purchase #4 $114.80   7.108%   $122.96   $122.96   $122.95   $123.00  
  Purchase #5 $210.80   4.295%   $219.8539   $219.85   $219.85   $219.90  
  Purchase #6 $215.81   3.770%   $223.946   $223.95   $223.95   $223.90  
  Purchase #7 $55.96   3.321%   $57.8184   $57.82   $57.80   $57.80  
  7 purchase totals = $967.61       $1,024.1276   $1,024.13   $1,024.05   $1,024.10