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 $48.94   13.786%   $55.6869   $55.69   $55.70   $55.70  
  Purchase #2 $198.69   3.184%   $205.0163   $205.02   $205.00   $205.00  
  Purchase #3 $140.33   13.715%   $159.5763   $159.58   $159.60   $159.60  
  Purchase #4 $173.47   11.283%   $193.0426   $193.04   $193.05   $193.00  
  Purchase #5 $54.95   10.575%   $60.761   $60.76   $60.75   $60.80  
  Purchase #6 $137.63   4.358%   $143.6279   $143.63   $143.65   $143.60  
  Purchase #7 $67.70   11.582%   $75.541   $75.54   $75.55   $75.50  
  7 purchase totals = $821.71       $893.2520   $893.26   $893.30   $893.20