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 $241.52   11.214%   $268.6041   $268.60   $268.60   $268.60  
  Purchase #2 $79.66   13.232%   $90.2006   $90.20   $90.20   $90.20  
  Purchase #3 $19.91   7.639%   $21.4309   $21.43   $21.45   $21.40  
  Purchase #4 $172.58   11.800%   $192.9444   $192.94   $192.95   $192.90  
  Purchase #5 $231.95   4.322%   $241.9749   $241.97   $241.95   $242.00  
  Purchase #6 $228.58   10.683%   $252.9992   $253.00   $253.00   $253.00  
  Purchase #7 $140.70   6.693%   $150.1171   $150.12   $150.10   $150.10  
  7 purchase totals = $1,114.90       $1,218.2712   $1,218.26   $1,218.25   $1,218.20