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 $234.47   7.481%   $252.0107   $252.01   $252.00   $252.00  
  Purchase #2 $101.56   4.572%   $106.2033   $106.20   $106.20   $106.20  
  Purchase #3 $120.95   8.753%   $131.5368   $131.54   $131.55   $131.50  
  Purchase #4 $44.69   6.272%   $47.493   $47.49   $47.50   $47.50  
  Purchase #5 $187.26   10.814%   $207.5103   $207.51   $207.50   $207.50  
  Purchase #6 $61.45   3.543%   $63.6272   $63.63   $63.65   $63.60  
  Purchase #7 $82.79   13.823%   $94.2341   $94.23   $94.25   $94.20  
  7 purchase totals = $833.17       $902.6154   $902.61   $902.65   $902.50