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 $248.31   5.803%   $262.7194   $262.72   $262.70   $262.70  
  Purchase #2 $109.56   12.517%   $123.2736   $123.27   $123.25   $123.30  
  Purchase #3 $120.27   3.127%   $124.0308   $124.03   $124.05   $124.00  
  Purchase #4 $95.89   5.523%   $101.186   $101.19   $101.20   $101.20  
  Purchase #5 $238.98   12.261%   $268.2813   $268.28   $268.30   $268.30  
  Purchase #6 $156.70   4.379%   $163.5619   $163.56   $163.55   $163.60  
  Purchase #7 $7.30   3.659%   $7.5671   $7.57   $7.55   $7.60  
  7 purchase totals = $977.01       $1,050.6201   $1,050.62   $1,050.60   $1,050.70