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 $64.42   9.673%   $70.6513   $70.65   $70.65   $70.70  
  Purchase #2 $180.56   11.830%   $201.9202   $201.92   $201.90   $201.90  
  Purchase #3 $185.49   7.403%   $199.2218   $199.22   $199.20   $199.20  
  Purchase #4 $7.75   5.870%   $8.2049   $8.20   $8.20   $8.20  
  Purchase #5 $123.33   13.712%   $140.241   $140.24   $140.25   $140.20  
  Purchase #6 $171.92   7.633%   $185.0427   $185.04   $185.05   $185.00  
  Purchase #7 $41.72   6.315%   $44.3546   $44.35   $44.35   $44.40  
  7 purchase totals = $775.19       $849.6365   $849.62   $849.60   $849.60