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 $115.57   8.422%   $125.3033   $125.30   $125.30   $125.30  
  Purchase #2 $70.37   6.534%   $74.968   $74.97   $74.95   $75.00  
  Purchase #3 $142.37   7.345%   $152.8271   $152.83   $152.85   $152.80  
  Purchase #4 $161.88   7.790%   $174.4905   $174.49   $174.50   $174.50  
  Purchase #5 $99.79   11.435%   $111.201   $111.20   $111.20   $111.20  
  Purchase #6 $76.88   6.848%   $82.1447   $82.14   $82.15   $82.10  
  Purchase #7 $23.62   3.369%   $24.4158   $24.42   $24.40   $24.40  
  7 purchase totals = $690.48       $745.3504   $745.35   $745.35   $745.30