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 $216.83   11.240%   $241.2017   $241.20   $241.20   $241.20  
  Purchase #2 $61.97   10.683%   $68.5903   $68.59   $68.60   $68.60  
  Purchase #3 $171.64   4.850%   $179.9645   $179.96   $179.95   $180.00  
  Purchase #4 $135.67   10.487%   $149.8977   $149.90   $149.90   $149.90  
  Purchase #5 $213.99   3.526%   $221.5353   $221.54   $221.55   $221.50  
  Purchase #6 $114.65   6.710%   $122.343   $122.34   $122.35   $122.30  
  Purchase #7 $68.89   5.452%   $72.6459   $72.65   $72.65   $72.60  
  7 purchase totals = $983.64       $1,056.1784   $1,056.18   $1,056.20   $1,056.10