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 $220.34   10.524%   $243.5286   $243.53   $243.55   $243.50  
  Purchase #2 $155.84   6.445%   $165.8839   $165.88   $165.90   $165.90  
  Purchase #3 $55.86   5.602%   $58.9893   $58.99   $59.00   $59.00  
  Purchase #4 $230.74   4.823%   $241.8686   $241.87   $241.85   $241.90  
  Purchase #5 $136.60   11.150%   $151.8309   $151.83   $151.85   $151.80  
  Purchase #6 $190.26   6.372%   $202.3834   $202.38   $202.40   $202.40  
  Purchase #7 $79.62   9.509%   $87.1911   $87.19   $87.20   $87.20  
  7 purchase totals = $1,069.26       $1,151.6758   $1,151.67   $1,151.75   $1,151.70