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 $71.49   6.515%   $76.1476   $76.15   $76.15   $76.10  
  Purchase #2 $250.62   10.402%   $276.6895   $276.69   $276.70   $276.70  
  Purchase #3 $149.81   4.766%   $156.9499   $156.95   $156.95   $156.90  
  Purchase #4 $165.65   8.601%   $179.8976   $179.90   $179.90   $179.90  
  Purchase #5 $126.98   3.528%   $131.4599   $131.46   $131.45   $131.50  
  Purchase #6 $225.70   6.108%   $239.4858   $239.49   $239.50   $239.50  
  Purchase #7 $55.58   13.337%   $62.9927   $62.99   $63.00   $63.00  
  7 purchase totals = $1,045.83       $1,123.6230   $1,123.63   $1,123.65   $1,123.60