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 $226.95   10.606%   $251.0203   $251.02   $251.00   $251.00  
  Purchase #2 $188.97   3.803%   $196.1565   $196.16   $196.15   $196.20  
  Purchase #3 $142.97   7.812%   $154.1388   $154.14   $154.15   $154.10  
  Purchase #4 $162.93   4.663%   $170.5274   $170.53   $170.55   $170.50  
  Purchase #5 $159.50   8.262%   $172.6779   $172.68   $172.70   $172.70  
  Purchase #6 $211.35   9.243%   $230.8851   $230.89   $230.90   $230.90  
  Purchase #7 $63.68   3.454%   $65.8795   $65.88   $65.90   $65.90  
  7 purchase totals = $1,156.35       $1,241.2855   $1,241.30   $1,241.35   $1,241.30