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 $63.57   13.107%   $71.9021   $71.90   $71.90   $71.90  
  Purchase #2 $163.81   5.839%   $173.3749   $173.37   $173.35   $173.40  
  Purchase #3 $156.95   10.348%   $173.1912   $173.19   $173.20   $173.20  
  Purchase #4 $249.61   6.860%   $266.7332   $266.73   $266.75   $266.70  
  Purchase #5 $9.28   4.255%   $9.6749   $9.67   $9.65   $9.70  
  Purchase #6 $81.80   4.275%   $85.297   $85.30   $85.30   $85.30  
  Purchase #7 $245.52   7.583%   $264.1378   $264.14   $264.15   $264.10  
  7 purchase totals = $970.54       $1,044.3111   $1,044.30   $1,044.30   $1,044.30