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 $208.58   8.174%   $225.6293   $225.63   $225.65   $225.60  
  Purchase #2 $157.92   12.268%   $177.2936   $177.29   $177.30   $177.30  
  Purchase #3 $54.70   4.379%   $57.0953   $57.10   $57.10   $57.10  
  Purchase #4 $163.54   4.401%   $170.7374   $170.74   $170.75   $170.70  
  Purchase #5 $95.35   10.414%   $105.2797   $105.28   $105.30   $105.30  
  Purchase #6 $43.26   12.411%   $48.629   $48.63   $48.65   $48.60  
  Purchase #7 $179.64   6.780%   $191.8196   $191.82   $191.80   $191.80  
  7 purchase totals = $902.99       $976.4839   $976.49   $976.55   $976.40