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 $37.88   9.517%   $41.485   $41.49   $41.50   $41.50  
  Purchase #2 $104.30   11.652%   $116.453   $116.45   $116.45   $116.50  
  Purchase #3 $118.70   5.352%   $125.0528   $125.05   $125.05   $125.10  
  Purchase #4 $209.90   7.738%   $226.1421   $226.14   $226.15   $226.10  
  Purchase #5 $218.55   13.187%   $247.3702   $247.37   $247.35   $247.40  
  Purchase #6 $248.97   6.168%   $264.3265   $264.33   $264.35   $264.30  
  Purchase #7 $34.84   9.212%   $38.0495   $38.05   $38.05   $38.00  
  7 purchase totals = $973.14       $1,058.8791   $1,058.88   $1,058.90   $1,058.90