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 $198.77   5.666%   $210.0323   $210.03   $210.05   $210.00  
  Purchase #2 $33.44   9.585%   $36.6452   $36.65   $36.65   $36.60  
  Purchase #3 $40.54   3.693%   $42.0371   $42.04   $42.05   $42.00  
  Purchase #4 $181.99   5.742%   $192.4399   $192.44   $192.45   $192.40  
  Purchase #5 $195.82   5.591%   $206.7683   $206.77   $206.75   $206.80  
  Purchase #6 $26.83   12.874%   $30.2841   $30.28   $30.30   $30.30  
  Purchase #7 $38.91   10.713%   $43.0784   $43.08   $43.10   $43.10  
  7 purchase totals = $716.30       $761.2853   $761.29   $761.35   $761.20