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 $35.99   6.159%   $38.2066   $38.21   $38.20   $38.20  
  Purchase #2 $241.75   11.419%   $269.3554   $269.36   $269.35   $269.40  
  Purchase #3 $170.92   8.168%   $184.8807   $184.88   $184.90   $184.90  
  Purchase #4 $51.74   7.597%   $55.6707   $55.67   $55.65   $55.70  
  Purchase #5 $35.63   11.263%   $39.643   $39.64   $39.65   $39.60  
  Purchase #6 $180.43   9.245%   $197.1108   $197.11   $197.10   $197.10  
  Purchase #7 $233.77   10.608%   $258.5683   $258.57   $258.55   $258.60  
  7 purchase totals = $950.23       $1,043.4355   $1,043.44   $1,043.40   $1,043.50