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 $235.32   13.838%   $267.8836   $267.88   $267.90   $267.90  
  Purchase #2 $185.31   9.193%   $202.3455   $202.35   $202.35   $202.30  
  Purchase #3 $112.46   11.711%   $125.6302   $125.63   $125.65   $125.60  
  Purchase #4 $65.57   4.132%   $68.2794   $68.28   $68.30   $68.30  
  Purchase #5 $241.80   11.365%   $269.2806   $269.28   $269.30   $269.30  
  Purchase #6 $15.48   11.746%   $17.2983   $17.30   $17.30   $17.30  
  Purchase #7 $80.81   9.579%   $88.5508   $88.55   $88.55   $88.60  
  7 purchase totals = $936.75       $1,039.2684   $1,039.27   $1,039.35   $1,039.30