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 $179.67   12.159%   $201.5161   $201.52   $201.50   $201.50  
  Purchase #2 $57.27   9.615%   $62.7765   $62.78   $62.80   $62.80  
  Purchase #3 $107.55   5.757%   $113.7417   $113.74   $113.75   $113.70  
  Purchase #4 $206.81   9.295%   $226.033   $226.03   $226.05   $226.00  
  Purchase #5 $56.28   8.287%   $60.9439   $60.94   $60.95   $60.90  
  Purchase #6 $211.40   4.486%   $220.8834   $220.88   $220.90   $220.90  
  Purchase #7 $69.52   10.676%   $76.942   $76.94   $76.95   $76.90  
  7 purchase totals = $888.50       $962.8366   $962.83   $962.90   $962.70