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 $189.43   9.460%   $207.3501   $207.35   $207.35   $207.40  
  Purchase #2 $130.76   10.613%   $144.6376   $144.64   $144.65   $144.60  
  Purchase #3 $158.80   8.852%   $172.857   $172.86   $172.85   $172.90  
  Purchase #4 $103.51   3.716%   $107.3564   $107.36   $107.35   $107.40  
  Purchase #5 $153.50   6.799%   $163.9365   $163.94   $163.95   $163.90  
  Purchase #6 $185.45   6.751%   $197.9697   $197.97   $197.95   $198.00  
  Purchase #7 $162.26   6.361%   $172.5814   $172.58   $172.60   $172.60  
  7 purchase totals = $1,083.71       $1,166.6887   $1,166.70   $1,166.70   $1,166.80