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 $94.89   11.616%   $105.9124   $105.91   $105.90   $105.90  
  Purchase #2 $34.79   4.352%   $36.3041   $36.30   $36.30   $36.30  
  Purchase #3 $217.31   3.345%   $224.579   $224.58   $224.60   $224.60  
  Purchase #4 $222.76   5.501%   $235.014   $235.01   $235.00   $235.00  
  Purchase #5 $69.91   13.258%   $79.1787   $79.18   $79.20   $79.20  
  Purchase #6 $138.84   4.153%   $144.606   $144.61   $144.60   $144.60  
  Purchase #7 $209.64   12.482%   $235.8073   $235.81   $235.80   $235.80  
  7 purchase totals = $988.14       $1,061.4015   $1,061.40   $1,061.40   $1,061.40