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 $64.29   10.423%   $70.9909   $70.99   $71.00   $71.00  
  Purchase #2 $170.76   8.782%   $185.7561   $185.76   $185.75   $185.80  
  Purchase #3 $241.70   8.275%   $261.7007   $261.70   $261.70   $261.70  
  Purchase #4 $83.77   11.787%   $93.644   $93.64   $93.65   $93.60  
  Purchase #5 $164.83   5.123%   $173.2742   $173.27   $173.25   $173.30  
  Purchase #6 $241.58   5.206%   $254.1567   $254.16   $254.15   $254.20  
  Purchase #7 $158.93   9.643%   $174.2556   $174.26   $174.25   $174.30  
  7 purchase totals = $1,125.86       $1,213.7782   $1,213.78   $1,213.75   $1,213.90