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 $234.67   12.163%   $263.2129   $263.21   $263.20   $263.20  
  Purchase #2 $116.48   9.267%   $127.2742   $127.27   $127.25   $127.30  
  Purchase #3 $223.44   7.642%   $240.5153   $240.52   $240.50   $240.50  
  Purchase #4 $66.71   5.538%   $70.4044   $70.40   $70.40   $70.40  
  Purchase #5 $42.65   10.297%   $47.0417   $47.04   $47.05   $47.00  
  Purchase #6 $26.67   9.244%   $29.1354   $29.14   $29.15   $29.10  
  Purchase #7 $167.80   11.854%   $187.691   $187.69   $187.70   $187.70  
  7 purchase totals = $878.42       $965.2749   $965.27   $965.25   $965.20