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 $144.43   4.708%   $151.2298   $151.23   $151.25   $151.20  
  Purchase #2 $226.45   13.413%   $256.8237   $256.82   $256.80   $256.80  
  Purchase #3 $158.80   9.602%   $174.048   $174.05   $174.05   $174.00  
  Purchase #4 $60.83   12.686%   $68.5469   $68.55   $68.55   $68.50  
  Purchase #5 $193.99   3.793%   $201.348   $201.35   $201.35   $201.30  
  Purchase #6 $203.81   11.378%   $226.9995   $227.00   $227.00   $227.00  
  Purchase #7 $145.62   13.501%   $165.2802   $165.28   $165.30   $165.30  
  7 purchase totals = $1,133.93       $1,244.2761   $1,244.28   $1,244.30   $1,244.10