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 $169.49   7.200%   $181.6933   $181.69   $181.70   $181.70  
  Purchase #2 $134.35   7.460%   $144.3725   $144.37   $144.35   $144.40  
  Purchase #3 $114.51   4.627%   $119.8084   $119.81   $119.80   $119.80  
  Purchase #4 $163.77   8.442%   $177.5955   $177.60   $177.60   $177.60  
  Purchase #5 $112.54   10.426%   $124.2734   $124.27   $124.25   $124.30  
  Purchase #6 $182.41   12.793%   $205.7457   $205.75   $205.75   $205.70  
  Purchase #7 $101.49   5.739%   $107.3145   $107.31   $107.30   $107.30  
  7 purchase totals = $978.56       $1,060.8033   $1,060.80   $1,060.75   $1,060.80