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 $196.79   8.479%   $213.4758   $213.48   $213.50   $213.50  
  Purchase #2 $184.42   11.819%   $206.2166   $206.22   $206.20   $206.20  
  Purchase #3 $34.80   11.148%   $38.6795   $38.68   $38.70   $38.70  
  Purchase #4 $188.48   4.445%   $196.8579   $196.86   $196.85   $196.90  
  Purchase #5 $115.94   11.798%   $129.6186   $129.62   $129.60   $129.60  
  Purchase #6 $23.91   10.570%   $26.4373   $26.44   $26.45   $26.40  
  Purchase #7 $236.42   9.418%   $258.686   $258.69   $258.70   $258.70  
  7 purchase totals = $980.76       $1,069.9717   $1,069.99   $1,070.00   $1,070.00