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 $9.83   13.341%   $11.1414   $11.14   $11.15   $11.10  
  Purchase #2 $226.52   6.620%   $241.5156   $241.52   $241.50   $241.50  
  Purchase #3 $219.79   10.544%   $242.9647   $242.96   $242.95   $243.00  
  Purchase #4 $166.30   3.408%   $171.9675   $171.97   $171.95   $172.00  
  Purchase #5 $224.93   7.697%   $242.2429   $242.24   $242.25   $242.20  
  Purchase #6 $227.43   12.727%   $256.375   $256.38   $256.40   $256.40  
  Purchase #7 $86.56   9.380%   $94.6793   $94.68   $94.70   $94.70  
  7 purchase totals = $1,161.36       $1,260.8864   $1,260.89   $1,260.90   $1,260.90