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 $30.37   11.289%   $33.7985   $33.80   $33.80   $33.80  
  Purchase #2 $219.83   8.678%   $238.9068   $238.91   $238.90   $238.90  
  Purchase #3 $135.95   8.322%   $147.2638   $147.26   $147.25   $147.30  
  Purchase #4 $207.49   4.462%   $216.7482   $216.75   $216.75   $216.70  
  Purchase #5 $196.84   13.343%   $223.1044   $223.10   $223.10   $223.10  
  Purchase #6 $219.70   13.124%   $248.5334   $248.53   $248.55   $248.50  
  Purchase #7 $62.92   7.490%   $67.6327   $67.63   $67.65   $67.60  
  7 purchase totals = $1,073.10       $1,175.9878   $1,175.98   $1,176.00   $1,175.90