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 $181.85   12.591%   $204.7467   $204.75   $204.75   $204.70  
  Purchase #2 $56.55   6.749%   $60.3666   $60.37   $60.35   $60.40  
  Purchase #3 $208.48   8.643%   $226.4989   $226.50   $226.50   $226.50  
  Purchase #4 $100.31   10.767%   $111.1104   $111.11   $111.10   $111.10  
  Purchase #5 $116.39   9.336%   $127.2562   $127.26   $127.25   $127.30  
  Purchase #6 $80.92   4.308%   $84.406   $84.41   $84.40   $84.40  
  Purchase #7 $10.51   10.718%   $11.6365   $11.64   $11.65   $11.60  
  7 purchase totals = $755.01       $826.0213   $826.04   $826.00   $826.00