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 $59.33   6.622%   $63.2588   $63.26   $63.25   $63.30  
  Purchase #2 $162.92   5.709%   $172.2211   $172.22   $172.20   $172.20  
  Purchase #3 $219.86   9.396%   $240.518   $240.52   $240.50   $240.50  
  Purchase #4 $111.37   13.518%   $126.425   $126.43   $126.45   $126.40  
  Purchase #5 $128.43   3.680%   $133.1562   $133.16   $133.15   $133.20  
  Purchase #6 $123.91   8.200%   $134.0706   $134.07   $134.05   $134.10  
  Purchase #7 $234.41   12.435%   $263.5589   $263.56   $263.55   $263.60  
  7 purchase totals = $1,040.23       $1,133.2086   $1,133.22   $1,133.15   $1,133.30