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 $22.53   13.455%   $25.5614   $25.56   $25.55   $25.60  
  Purchase #2 $232.91   13.162%   $263.5656   $263.57   $263.55   $263.60  
  Purchase #3 $25.94   10.181%   $28.581   $28.58   $28.60   $28.60  
  Purchase #4 $66.54   6.745%   $71.0281   $71.03   $71.05   $71.00  
  Purchase #5 $166.75   6.340%   $177.322   $177.32   $177.30   $177.30  
  Purchase #6 $177.63   13.521%   $201.6474   $201.65   $201.65   $201.60  
  Purchase #7 $178.68   3.176%   $184.3549   $184.35   $184.35   $184.40  
  7 purchase totals = $870.98       $952.0604   $952.06   $952.05   $952.10