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 $62.40   4.113%   $64.9665   $64.97   $64.95   $65.00  
  Purchase #2 $219.81   10.285%   $242.4175   $242.42   $242.40   $242.40  
  Purchase #3 $64.29   6.249%   $68.3075   $68.31   $68.30   $68.30  
  Purchase #4 $153.71   13.615%   $174.6376   $174.64   $174.65   $174.60  
  Purchase #5 $190.61   12.148%   $213.7653   $213.77   $213.75   $213.80  
  Purchase #6 $178.98   9.784%   $196.4914   $196.49   $196.50   $196.50  
  Purchase #7 $181.46   8.704%   $197.2543   $197.25   $197.25   $197.30  
  7 purchase totals = $1,051.26       $1,157.8401   $1,157.85   $1,157.80   $1,157.90