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 $191.76   8.608%   $208.2667   $208.27   $208.25   $208.30  
  Purchase #2 $96.33   12.823%   $108.6824   $108.68   $108.70   $108.70  
  Purchase #3 $115.30   6.754%   $123.0874   $123.09   $123.10   $123.10  
  Purchase #4 $202.96   10.534%   $224.3398   $224.34   $224.35   $224.30  
  Purchase #5 $139.29   8.674%   $151.372   $151.37   $151.35   $151.40  
  Purchase #6 $80.30   6.377%   $85.4207   $85.42   $85.40   $85.40  
  Purchase #7 $158.88   9.544%   $174.0435   $174.04   $174.05   $174.00  
  7 purchase totals = $984.82       $1,075.2125   $1,075.21   $1,075.20   $1,075.20