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 $37.76   5.469%   $39.8251   $39.83   $39.85   $39.80  
  Purchase #2 $129.43   7.498%   $139.1347   $139.13   $139.15   $139.10  
  Purchase #3 $12.76   4.246%   $13.3018   $13.30   $13.30   $13.30  
  Purchase #4 $126.70   12.323%   $142.3132   $142.31   $142.30   $142.30  
  Purchase #5 $128.96   7.534%   $138.6758   $138.68   $138.70   $138.70  
  Purchase #6 $96.82   9.809%   $106.3171   $106.32   $106.30   $106.30  
  Purchase #7 $38.50   10.865%   $42.683   $42.68   $42.70   $42.70  
  7 purchase totals = $570.93       $622.2507   $622.25   $622.30   $622.20