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 $187.65   8.443%   $203.4933   $203.49   $203.50   $203.50  
  Purchase #2 $33.66   5.332%   $35.4548   $35.45   $35.45   $35.50  
  Purchase #3 $66.37   5.468%   $69.9991   $70.00   $70.00   $70.00  
  Purchase #4 $187.81   8.149%   $203.1146   $203.11   $203.10   $203.10  
  Purchase #5 $95.42   8.509%   $103.5393   $103.54   $103.55   $103.50  
  Purchase #6 $164.96   7.291%   $176.9872   $176.99   $177.00   $177.00  
  Purchase #7 $196.86   13.361%   $223.1625   $223.16   $223.15   $223.20  
  7 purchase totals = $932.73       $1,015.7508   $1,015.74   $1,015.75   $1,015.80