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 $33.83   11.220%   $37.6257   $37.63   $37.65   $37.60  
  Purchase #2 $77.64   5.188%   $81.668   $81.67   $81.65   $81.70  
  Purchase #3 $122.84   9.609%   $134.6437   $134.64   $134.65   $134.60  
  Purchase #4 $237.66   6.872%   $253.992   $253.99   $254.00   $254.00  
  Purchase #5 $85.66   7.441%   $92.034   $92.03   $92.05   $92.00  
  Purchase #6 $61.93   9.716%   $67.9471   $67.95   $67.95   $67.90  
  Purchase #7 $71.68   11.111%   $79.6444   $79.64   $79.65   $79.60  
  7 purchase totals = $691.24       $747.5549   $747.55   $747.60   $747.40