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 $68.30   13.522%   $77.5355   $77.54   $77.55   $77.50  
  Purchase #2 $78.47   5.614%   $82.8753   $82.88   $82.90   $82.90  
  Purchase #3 $35.25   8.607%   $38.284   $38.28   $38.30   $38.30  
  Purchase #4 $9.58   13.204%   $10.8449   $10.84   $10.85   $10.80  
  Purchase #5 $148.65   5.142%   $156.2936   $156.29   $156.30   $156.30  
  Purchase #6 $229.59   9.350%   $251.0567   $251.06   $251.05   $251.10  
  Purchase #7 $89.74   5.855%   $94.9943   $94.99   $95.00   $95.00  
  7 purchase totals = $659.58       $711.8843   $711.88   $711.95   $711.90