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 $57.85   10.504%   $63.9266   $63.93   $63.95   $63.90  
  Purchase #2 $42.25   7.441%   $45.3938   $45.39   $45.40   $45.40  
  Purchase #3 $136.83   5.720%   $144.6567   $144.66   $144.65   $144.70  
  Purchase #4 $53.50   8.481%   $58.0373   $58.04   $58.05   $58.00  
  Purchase #5 $46.36   11.590%   $51.7331   $51.73   $51.75   $51.70  
  Purchase #6 $99.87   6.373%   $106.2347   $106.23   $106.25   $106.20  
  Purchase #7 $240.29   5.331%   $253.0999   $253.10   $253.10   $253.10  
  7 purchase totals = $676.95       $723.0821   $723.08   $723.15   $723.00