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 $75.99   10.623%   $84.0624   $84.06   $84.05   $84.10  
  Purchase #2 $182.73   9.202%   $199.5448   $199.54   $199.55   $199.50  
  Purchase #3 $233.50   8.708%   $253.8332   $253.83   $253.85   $253.80  
  Purchase #4 $203.61   6.352%   $216.5433   $216.54   $216.55   $216.50  
  Purchase #5 $32.76   9.836%   $35.9823   $35.98   $36.00   $36.00  
  Purchase #6 $26.91   9.266%   $29.4035   $29.40   $29.40   $29.40  
  Purchase #7 $98.92   8.167%   $106.9988   $107.00   $107.00   $107.00  
  7 purchase totals = $854.42       $926.3683   $926.35   $926.40   $926.30