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 $51.52   8.267%   $55.7792   $55.78   $55.80   $55.80  
  Purchase #2 $164.76   7.462%   $177.0544   $177.05   $177.05   $177.10  
  Purchase #3 $235.71   11.181%   $262.0647   $262.06   $262.05   $262.10  
  Purchase #4 $37.37   11.391%   $41.6268   $41.63   $41.65   $41.60  
  Purchase #5 $145.94   3.721%   $151.3704   $151.37   $151.35   $151.40  
  Purchase #6 $199.99   4.639%   $209.2675   $209.27   $209.25   $209.30  
  Purchase #7 $121.51   6.339%   $129.2125   $129.21   $129.20   $129.20  
  7 purchase totals = $956.80       $1,026.3755   $1,026.37   $1,026.35   $1,026.50