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 $207.97   13.643%   $236.3433   $236.34   $236.35   $236.30  
  Purchase #2 $14.70   11.322%   $16.3643   $16.36   $16.35   $16.40  
  Purchase #3 $105.93   11.627%   $118.2465   $118.25   $118.25   $118.20  
  Purchase #4 $95.52   11.584%   $106.585   $106.59   $106.60   $106.60  
  Purchase #5 $124.39   5.307%   $130.9914   $130.99   $131.00   $131.00  
  Purchase #6 $147.91   12.244%   $166.0201   $166.02   $166.00   $166.00  
  Purchase #7 $176.77   9.207%   $193.0452   $193.05   $193.05   $193.00  
  7 purchase totals = $873.19       $967.5958   $967.60   $967.60   $967.50