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 $109.42   4.503%   $114.3472   $114.35   $114.35   $114.30  
  Purchase #2 $206.25   5.231%   $217.0389   $217.04   $217.05   $217.00  
  Purchase #3 $140.56   8.396%   $152.3614   $152.36   $152.35   $152.40  
  Purchase #4 $29.74   11.368%   $33.1208   $33.12   $33.10   $33.10  
  Purchase #5 $186.37   10.352%   $205.663   $205.66   $205.65   $205.70  
  Purchase #6 $119.55   12.315%   $134.2726   $134.27   $134.25   $134.30  
  Purchase #7 $156.31   12.628%   $176.0488   $176.05   $176.05   $176.00  
  7 purchase totals = $948.20       $1,032.8527   $1,032.85   $1,032.80   $1,032.80