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 $202.76   11.126%   $225.3191   $225.32   $225.30   $225.30  
  Purchase #2 $236.91   13.821%   $269.6533   $269.65   $269.65   $269.70  
  Purchase #3 $26.92   7.381%   $28.907   $28.91   $28.90   $28.90  
  Purchase #4 $86.43   13.656%   $98.2329   $98.23   $98.25   $98.20  
  Purchase #5 $158.49   13.586%   $180.0225   $180.02   $180.00   $180.00  
  Purchase #6 $125.53   12.218%   $140.8673   $140.87   $140.85   $140.90  
  Purchase #7 $170.72   13.386%   $193.5726   $193.57   $193.55   $193.60  
  7 purchase totals = $1,007.76       $1,136.5747   $1,136.57   $1,136.50   $1,136.60