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 $31.69   6.598%   $33.7809   $33.78   $33.80   $33.80  
  Purchase #2 $172.46   11.574%   $192.4205   $192.42   $192.40   $192.40  
  Purchase #3 $152.59   13.725%   $173.533   $173.53   $173.55   $173.50  
  Purchase #4 $231.81   8.571%   $251.6784   $251.68   $251.70   $251.70  
  Purchase #5 $6.78   9.755%   $7.4414   $7.44   $7.45   $7.40  
  Purchase #6 $59.48   11.218%   $66.1525   $66.15   $66.15   $66.20  
  Purchase #7 $230.48   7.656%   $248.1255   $248.13   $248.15   $248.10  
  7 purchase totals = $885.29       $973.1322   $973.13   $973.20   $973.10