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 $126.94   11.326%   $141.3172   $141.32   $141.30   $141.30  
  Purchase #2 $107.66   5.544%   $113.6287   $113.63   $113.65   $113.60  
  Purchase #3 $38.88   7.554%   $41.817   $41.82   $41.80   $41.80  
  Purchase #4 $102.32   12.673%   $115.287   $115.29   $115.30   $115.30  
  Purchase #5 $180.67   12.116%   $202.56   $202.56   $202.55   $202.60  
  Purchase #6 $229.64   8.182%   $248.4291   $248.43   $248.45   $248.40  
  Purchase #7 $206.48   11.348%   $229.9114   $229.91   $229.90   $229.90  
  7 purchase totals = $992.59       $1,092.9504   $1,092.96   $1,092.95   $1,092.90