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 $194.78   6.774%   $207.9744   $207.97   $207.95   $208.00  
  Purchase #2 $52.72   3.558%   $54.5958   $54.60   $54.60   $54.60  
  Purchase #3 $100.65   11.698%   $112.424   $112.42   $112.40   $112.40  
  Purchase #4 $125.32   3.316%   $129.4756   $129.48   $129.50   $129.50  
  Purchase #5 $137.47   7.591%   $147.9053   $147.91   $147.90   $147.90  
  Purchase #6 $151.76   6.127%   $161.0583   $161.06   $161.05   $161.10  
  Purchase #7 $116.76   7.258%   $125.2344   $125.23   $125.25   $125.20  
  7 purchase totals = $879.46       $938.6678   $938.67   $938.65   $938.70