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 $202.45   3.509%   $209.554   $209.55   $209.55   $209.60  
  Purchase #2 $15.42   7.436%   $16.5666   $16.57   $16.55   $16.60  
  Purchase #3 $28.72   10.606%   $31.766   $31.77   $31.75   $31.80  
  Purchase #4 $99.67   6.603%   $106.2512   $106.25   $106.25   $106.30  
  Purchase #5 $168.35   5.446%   $177.5183   $177.52   $177.50   $177.50  
  Purchase #6 $248.79   5.770%   $263.1452   $263.15   $263.15   $263.10  
  Purchase #7 $66.87   10.464%   $73.8673   $73.87   $73.85   $73.90  
  7 purchase totals = $830.27       $878.6686   $878.68   $878.60   $878.80