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 $161.47   12.641%   $181.8814   $181.88   $181.90   $181.90  
  Purchase #2 $60.61   10.858%   $67.191   $67.19   $67.20   $67.20  
  Purchase #3 $203.96   13.866%   $232.2411   $232.24   $232.25   $232.20  
  Purchase #4 $144.81   4.281%   $151.0093   $151.01   $151.00   $151.00  
  Purchase #5 $27.97   4.487%   $29.225   $29.23   $29.25   $29.20  
  Purchase #6 $245.65   6.575%   $261.8015   $261.80   $261.80   $261.80  
  Purchase #7 $77.69   11.566%   $86.6756   $86.68   $86.70   $86.70  
  7 purchase totals = $922.16       $1,010.0249   $1,010.03   $1,010.10   $1,010.00