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 $108.78   4.273%   $113.4282   $113.43   $113.45   $113.40  
  Purchase #2 $11.52   8.469%   $12.4956   $12.50   $12.50   $12.50  
  Purchase #3 $60.82   6.631%   $64.853   $64.85   $64.85   $64.90  
  Purchase #4 $53.75   7.493%   $57.7775   $57.78   $57.80   $57.80  
  Purchase #5 $185.66   4.226%   $193.506   $193.51   $193.50   $193.50  
  Purchase #6 $218.86   4.114%   $227.8639   $227.86   $227.85   $227.90  
  Purchase #7 $163.26   13.315%   $184.9981   $185.00   $185.00   $185.00  
  7 purchase totals = $802.65       $854.9223   $854.93   $854.95   $855.00