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 $65.41   6.332%   $69.5518   $69.55   $69.55   $69.60  
  Purchase #2 $147.73   13.738%   $168.0251   $168.03   $168.05   $168.00  
  Purchase #3 $225.96   11.853%   $252.743   $252.74   $252.75   $252.70  
  Purchase #4 $48.96   8.353%   $53.0496   $53.05   $53.05   $53.00  
  Purchase #5 $55.90   9.787%   $61.3709   $61.37   $61.35   $61.40  
  Purchase #6 $171.58   13.262%   $194.3349   $194.33   $194.35   $194.30  
  Purchase #7 $64.44   3.609%   $66.7656   $66.77   $66.75   $66.80  
  7 purchase totals = $779.98       $865.8409   $865.84   $865.85   $865.80