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 $169.34   8.479%   $183.6983   $183.70   $183.70   $183.70  
  Purchase #2 $74.44   4.472%   $77.769   $77.77   $77.75   $77.80  
  Purchase #3 $186.77   5.698%   $197.4122   $197.41   $197.40   $197.40  
  Purchase #4 $30.76   8.847%   $33.4813   $33.48   $33.50   $33.50  
  Purchase #5 $199.58   3.213%   $205.9925   $205.99   $206.00   $206.00  
  Purchase #6 $175.80   12.668%   $198.0703   $198.07   $198.05   $198.10  
  Purchase #7 $112.27   3.516%   $116.2174   $116.22   $116.20   $116.20  
  7 purchase totals = $948.96       $1,012.6410   $1,012.64   $1,012.60   $1,012.70