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 $21.59   13.838%   $24.5776   $24.58   $24.60   $24.60  
  Purchase #2 $199.70   11.640%   $222.9451   $222.95   $222.95   $222.90  
  Purchase #3 $78.44   9.601%   $85.971   $85.97   $85.95   $86.00  
  Purchase #4 $41.86   3.347%   $43.2611   $43.26   $43.25   $43.30  
  Purchase #5 $160.58   9.167%   $175.3004   $175.30   $175.30   $175.30  
  Purchase #6 $153.59   9.248%   $167.794   $167.79   $167.80   $167.80  
  Purchase #7 $245.77   6.517%   $261.7868   $261.79   $261.80   $261.80  
  7 purchase totals = $901.53       $981.6360   $981.64   $981.65   $981.70