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 $34.42   6.553%   $36.6755   $36.68   $36.70   $36.70  
  Purchase #2 $212.96   4.242%   $221.9938   $221.99   $222.00   $222.00  
  Purchase #3 $242.91   3.777%   $252.0847   $252.08   $252.10   $252.10  
  Purchase #4 $184.53   5.300%   $194.3101   $194.31   $194.30   $194.30  
  Purchase #5 $12.83   6.578%   $13.674   $13.67   $13.65   $13.70  
  Purchase #6 $240.78   13.747%   $273.88   $273.88   $273.90   $273.90  
  Purchase #7 $217.33   7.777%   $234.2318   $234.23   $234.25   $234.20  
  7 purchase totals = $1,145.76       $1,226.8499   $1,226.84   $1,226.90   $1,226.90