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 $248.41   11.163%   $276.14   $276.14   $276.15   $276.10  
  Purchase #2 $58.87   13.124%   $66.5961   $66.60   $66.60   $66.60  
  Purchase #3 $44.52   13.134%   $50.3673   $50.37   $50.35   $50.40  
  Purchase #4 $77.47   3.851%   $80.4534   $80.45   $80.45   $80.50  
  Purchase #5 $160.85   6.708%   $171.6398   $171.64   $171.65   $171.60  
  Purchase #6 $233.69   7.602%   $251.4551   $251.46   $251.45   $251.50  
  Purchase #7 $106.69   6.802%   $113.9471   $113.95   $113.95   $113.90  
  7 purchase totals = $930.50       $1,010.5988   $1,010.61   $1,010.60   $1,010.60