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 $178.58   11.614%   $199.3203   $199.32   $199.30   $199.30  
  Purchase #2 $55.87   8.327%   $60.5223   $60.52   $60.50   $60.50  
  Purchase #3 $36.91   9.719%   $40.4973   $40.50   $40.50   $40.50  
  Purchase #4 $204.91   10.629%   $226.6899   $226.69   $226.70   $226.70  
  Purchase #5 $43.83   9.231%   $47.8759   $47.88   $47.90   $47.90  
  Purchase #6 $83.53   4.206%   $87.0433   $87.04   $87.05   $87.00  
  Purchase #7 $211.64   10.277%   $233.3902   $233.39   $233.40   $233.40  
  7 purchase totals = $815.27       $895.3392   $895.34   $895.35   $895.30