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 $197.65   13.593%   $224.5166   $224.52   $224.50   $224.50  
  Purchase #2 $82.66   3.241%   $85.339   $85.34   $85.35   $85.30  
  Purchase #3 $113.62   6.863%   $121.4177   $121.42   $121.40   $121.40  
  Purchase #4 $79.47   9.523%   $87.0379   $87.04   $87.05   $87.00  
  Purchase #5 $238.48   10.379%   $263.2318   $263.23   $263.25   $263.20  
  Purchase #6 $233.95   12.475%   $263.1353   $263.14   $263.15   $263.10  
  Purchase #7 $141.35   7.290%   $151.6544   $151.65   $151.65   $151.70  
  7 purchase totals = $1,087.18       $1,196.3327   $1,196.34   $1,196.35   $1,196.20