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 $214.62   8.244%   $232.3133   $232.31   $232.30   $232.30  
  Purchase #2 $243.80   6.616%   $259.9298   $259.93   $259.95   $259.90  
  Purchase #3 $30.96   4.833%   $32.4563   $32.46   $32.45   $32.50  
  Purchase #4 $127.50   13.453%   $144.6526   $144.65   $144.65   $144.70  
  Purchase #5 $189.80   8.259%   $205.4756   $205.48   $205.50   $205.50  
  Purchase #6 $72.81   11.851%   $81.4387   $81.44   $81.45   $81.40  
  Purchase #7 $117.94   3.434%   $121.9901   $121.99   $122.00   $122.00  
  7 purchase totals = $997.43       $1,078.2564   $1,078.26   $1,078.30   $1,078.30