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 $38.62   12.604%   $43.4877   $43.49   $43.50   $43.50  
  Purchase #2 $127.98   6.198%   $135.9122   $135.91   $135.90   $135.90  
  Purchase #3 $156.55   7.535%   $168.346   $168.35   $168.35   $168.30  
  Purchase #4 $190.27   3.536%   $196.9979   $197.00   $197.00   $197.00  
  Purchase #5 $5.69   10.148%   $6.2674   $6.27   $6.25   $6.30  
  Purchase #6 $204.53   10.232%   $225.4575   $225.46   $225.45   $225.50  
  Purchase #7 $223.99   9.142%   $244.4672   $244.47   $244.45   $244.50  
  7 purchase totals = $947.63       $1,020.9359   $1,020.95   $1,020.90   $1,021.00