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 $60.32   11.117%   $67.0258   $67.03   $67.05   $67.00  
  Purchase #2 $107.85   7.145%   $115.5559   $115.56   $115.55   $115.60  
  Purchase #3 $106.40   13.456%   $120.7172   $120.72   $120.70   $120.70  
  Purchase #4 $34.63   10.313%   $38.2014   $38.20   $38.20   $38.20  
  Purchase #5 $64.68   9.226%   $70.6474   $70.65   $70.65   $70.60  
  Purchase #6 $176.44   6.384%   $187.7039   $187.70   $187.70   $187.70  
  Purchase #7 $16.62   4.356%   $17.344   $17.34   $17.35   $17.30  
  7 purchase totals = $566.94       $617.1956   $617.20   $617.20   $617.10