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 $216.94   10.772%   $240.3088   $240.31   $240.30   $240.30  
  Purchase #2 $63.29   11.629%   $70.65   $70.65   $70.65   $70.70  
  Purchase #3 $171.61   9.121%   $187.2625   $187.26   $187.25   $187.30  
  Purchase #4 $210.82   7.467%   $226.5619   $226.56   $226.55   $226.60  
  Purchase #5 $113.51   11.291%   $126.3264   $126.33   $126.35   $126.30  
  Purchase #6 $104.91   7.849%   $113.1444   $113.14   $113.15   $113.10  
  Purchase #7 $56.96   11.757%   $63.6568   $63.66   $63.65   $63.70  
  7 purchase totals = $938.04       $1,027.9108   $1,027.91   $1,027.90   $1,028.00