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 $60.44   5.270%   $63.6252   $63.63   $63.65   $63.60  
  Purchase #2 $207.33   10.153%   $228.3802   $228.38   $228.40   $228.40  
  Purchase #3 $165.33   8.218%   $178.9168   $178.92   $178.90   $178.90  
  Purchase #4 $176.73   12.791%   $199.3355   $199.34   $199.35   $199.30  
  Purchase #5 $44.43   11.390%   $49.4906   $49.49   $49.50   $49.50  
  Purchase #6 $180.75   7.655%   $194.5864   $194.59   $194.60   $194.60  
  Purchase #7 $13.80   6.311%   $14.6709   $14.67   $14.65   $14.70  
  7 purchase totals = $848.81       $929.0056   $929.02   $929.05   $929.00