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 $136.56   12.783%   $154.0165   $154.02   $154.00   $154.00  
  Purchase #2 $108.74   6.222%   $115.5058   $115.51   $115.50   $115.50  
  Purchase #3 $216.38   4.438%   $225.9829   $225.98   $226.00   $226.00  
  Purchase #4 $35.46   7.751%   $38.2085   $38.21   $38.20   $38.20  
  Purchase #5 $54.29   8.322%   $58.808   $58.81   $58.80   $58.80  
  Purchase #6 $154.56   11.646%   $172.5601   $172.56   $172.55   $172.60  
  Purchase #7 $248.85   11.820%   $278.2641   $278.26   $278.25   $278.30  
  7 purchase totals = $954.84       $1,043.3459   $1,043.35   $1,043.30   $1,043.40