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 $65.98   13.181%   $74.6768   $74.68   $74.70   $74.70  
  Purchase #2 $226.33   6.239%   $240.4507   $240.45   $240.45   $240.50  
  Purchase #3 $121.62   4.353%   $126.9141   $126.91   $126.90   $126.90  
  Purchase #4 $140.88   8.441%   $152.7717   $152.77   $152.75   $152.80  
  Purchase #5 $14.71   9.702%   $16.1372   $16.14   $16.15   $16.10  
  Purchase #6 $191.57   4.700%   $200.5738   $200.57   $200.55   $200.60  
  Purchase #7 $188.67   10.487%   $208.4558   $208.46   $208.45   $208.50  
  7 purchase totals = $949.76       $1,019.9801   $1,019.98   $1,019.95   $1,020.10