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 $39.68   3.272%   $40.9783   $40.98   $41.00   $41.00  
  Purchase #2 $240.84   3.127%   $248.3711   $248.37   $248.35   $248.40  
  Purchase #3 $194.98   5.517%   $205.737   $205.74   $205.75   $205.70  
  Purchase #4 $71.77   12.664%   $80.859   $80.86   $80.85   $80.90  
  Purchase #5 $182.61   10.851%   $202.425   $202.43   $202.45   $202.40  
  Purchase #6 $148.31   11.587%   $165.4947   $165.49   $165.50   $165.50  
  Purchase #7 $34.34   12.563%   $38.6541   $38.65   $38.65   $38.70  
  7 purchase totals = $912.53       $982.5192   $982.52   $982.55   $982.60