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 $57.48   13.654%   $65.3283   $65.33   $65.35   $65.30  
  Purchase #2 $241.49   8.598%   $262.2533   $262.25   $262.25   $262.30  
  Purchase #3 $230.63   9.340%   $252.1708   $252.17   $252.15   $252.20  
  Purchase #4 $25.96   10.637%   $28.7214   $28.72   $28.70   $28.70  
  Purchase #5 $147.87   5.137%   $155.4661   $155.47   $155.45   $155.50  
  Purchase #6 $161.69   6.491%   $172.1853   $172.19   $172.20   $172.20  
  Purchase #7 $196.70   5.513%   $207.5441   $207.54   $207.55   $207.50  
  7 purchase totals = $1,061.82       $1,143.6693   $1,143.67   $1,143.65   $1,143.70