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 $114.41   4.142%   $119.1489   $119.15   $119.15   $119.10  
  Purchase #2 $204.67   6.413%   $217.7955   $217.80   $217.80   $217.80  
  Purchase #3 $171.50   8.755%   $186.5148   $186.51   $186.50   $186.50  
  Purchase #4 $17.41   13.601%   $19.7779   $19.78   $19.80   $19.80  
  Purchase #5 $193.73   6.167%   $205.6773   $205.68   $205.70   $205.70  
  Purchase #6 $87.77   13.490%   $99.6102   $99.61   $99.60   $99.60  
  Purchase #7 $188.58   11.608%   $210.4704   $210.47   $210.45   $210.50  
  7 purchase totals = $978.07       $1,058.9950   $1,059.00   $1,059.00   $1,059.00