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 $61.70   8.634%   $67.0272   $67.03   $67.05   $67.00  
  Purchase #2 $211.35   10.714%   $233.994   $233.99   $234.00   $234.00  
  Purchase #3 $65.61   11.360%   $73.0633   $73.06   $73.05   $73.10  
  Purchase #4 $169.67   13.488%   $192.5551   $192.56   $192.55   $192.60  
  Purchase #5 $84.92   3.236%   $87.668   $87.67   $87.65   $87.70  
  Purchase #6 $13.72   10.319%   $15.1358   $15.14   $15.15   $15.10  
  Purchase #7 $112.90   8.156%   $122.1081   $122.11   $122.10   $122.10  
  7 purchase totals = $719.87       $791.5515   $791.56   $791.55   $791.60