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 $41.66   4.355%   $43.4743   $43.47   $43.45   $43.50  
  Purchase #2 $101.92   13.310%   $115.4856   $115.49   $115.50   $115.50  
  Purchase #3 $212.49   4.176%   $221.3636   $221.36   $221.35   $221.40  
  Purchase #4 $97.27   9.852%   $106.853   $106.85   $106.85   $106.90  
  Purchase #5 $5.85   4.814%   $6.1316   $6.13   $6.15   $6.10  
  Purchase #6 $212.81   8.477%   $230.8499   $230.85   $230.85   $230.80  
  Purchase #7 $47.78   7.334%   $51.2842   $51.28   $51.30   $51.30  
  7 purchase totals = $719.78       $775.4422   $775.43   $775.45   $775.50