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 $36.74   4.644%   $38.4462   $38.45   $38.45   $38.40  
  Purchase #2 $171.60   3.461%   $177.5391   $177.54   $177.55   $177.50  
  Purchase #3 $170.72   12.621%   $192.2666   $192.27   $192.25   $192.30  
  Purchase #4 $201.68   10.614%   $223.0863   $223.09   $223.10   $223.10  
  Purchase #5 $11.44   11.520%   $12.7579   $12.76   $12.75   $12.80  
  Purchase #6 $147.70   4.604%   $154.5001   $154.50   $154.50   $154.50  
  Purchase #7 $148.89   9.822%   $163.514   $163.51   $163.50   $163.50  
  7 purchase totals = $888.77       $962.1102   $962.12   $962.10   $962.10