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 $58.68   11.751%   $65.5755   $65.58   $65.60   $65.60  
  Purchase #2 $164.61   8.261%   $178.2084   $178.21   $178.20   $178.20  
  Purchase #3 $19.62   11.434%   $21.8634   $21.86   $21.85   $21.90  
  Purchase #4 $207.99   5.548%   $219.5293   $219.53   $219.55   $219.50  
  Purchase #5 $177.52   7.858%   $191.4695   $191.47   $191.45   $191.50  
  Purchase #6 $201.71   10.782%   $223.4584   $223.46   $223.45   $223.50  
  Purchase #7 $133.66   5.416%   $140.899   $140.90   $140.90   $140.90  
  7 purchase totals = $963.79       $1,041.0035   $1,041.01   $1,041.00   $1,041.10