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 $84.80   9.305%   $92.6906   $92.69   $92.70   $92.70  
  Purchase #2 $216.70   9.855%   $238.0558   $238.06   $238.05   $238.10  
  Purchase #3 $65.68   7.695%   $70.7341   $70.73   $70.75   $70.70  
  Purchase #4 $242.67   11.615%   $270.8561   $270.86   $270.85   $270.90  
  Purchase #5 $126.91   13.461%   $143.9934   $143.99   $144.00   $144.00  
  Purchase #6 $49.31   11.772%   $55.1148   $55.11   $55.10   $55.10  
  Purchase #7 $68.62   11.218%   $76.3178   $76.32   $76.30   $76.30  
  7 purchase totals = $854.69       $947.7626   $947.76   $947.75   $947.80