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 $243.52   10.767%   $269.7398   $269.74   $269.75   $269.70  
  Purchase #2 $96.92   5.275%   $102.0325   $102.03   $102.05   $102.00  
  Purchase #3 $81.98   9.538%   $89.7993   $89.80   $89.80   $89.80  
  Purchase #4 $35.46   5.693%   $37.4787   $37.48   $37.50   $37.50  
  Purchase #5 $245.78   8.728%   $267.2317   $267.23   $267.25   $267.20  
  Purchase #6 $181.81   13.754%   $206.8161   $206.82   $206.80   $206.80  
  Purchase #7 $87.99   4.430%   $91.888   $91.89   $91.90   $91.90  
  7 purchase totals = $973.46       $1,064.9861   $1,064.99   $1,065.05   $1,064.90