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 $10.57   3.750%   $10.9664   $10.97   $10.95   $11.00  
  Purchase #2 $74.64   8.248%   $80.7963   $80.80   $80.80   $80.80  
  Purchase #3 $176.67   8.586%   $191.8389   $191.84   $191.85   $191.80  
  Purchase #4 $250.43   11.387%   $278.9465   $278.95   $278.95   $278.90  
  Purchase #5 $71.50   7.104%   $76.5794   $76.58   $76.60   $76.60  
  Purchase #6 $19.75   13.849%   $22.4852   $22.49   $22.50   $22.50  
  Purchase #7 $9.29   12.798%   $10.4789   $10.48   $10.50   $10.50  
  7 purchase totals = $612.85       $672.0916   $672.11   $672.15   $672.10