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 $119.98   10.295%   $132.3319   $132.33   $132.35   $132.30  
  Purchase #2 $114.98   9.815%   $126.2653   $126.27   $126.25   $126.30  
  Purchase #3 $192.41   4.421%   $200.9164   $200.92   $200.90   $200.90  
  Purchase #4 $11.78   6.664%   $12.565   $12.57   $12.55   $12.60  
  Purchase #5 $182.26   12.669%   $205.3505   $205.35   $205.35   $205.40  
  Purchase #6 $203.74   4.815%   $213.5501   $213.55   $213.55   $213.60  
  Purchase #7 $106.51   11.163%   $118.3997   $118.40   $118.40   $118.40  
  7 purchase totals = $931.66       $1,009.3789   $1,009.39   $1,009.35   $1,009.50