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 $90.98   5.587%   $96.0631   $96.06   $96.05   $96.10  
  Purchase #2 $33.85   10.448%   $37.3866   $37.39   $37.40   $37.40  
  Purchase #3 $191.99   6.108%   $203.7167   $203.72   $203.70   $203.70  
  Purchase #4 $231.85   10.539%   $256.2847   $256.28   $256.30   $256.30  
  Purchase #5 $11.88   6.665%   $12.6718   $12.67   $12.65   $12.70  
  Purchase #6 $153.32   5.679%   $162.027   $162.03   $162.05   $162.00  
  Purchase #7 $244.97   11.697%   $273.6241   $273.62   $273.60   $273.60  
  7 purchase totals = $958.84       $1,041.7740   $1,041.77   $1,041.75   $1,041.80