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 $41.94   3.821%   $43.5425   $43.54   $43.55   $43.50  
  Purchase #2 $239.62   7.657%   $257.9677   $257.97   $257.95   $258.00  
  Purchase #3 $123.86   11.710%   $138.364   $138.36   $138.35   $138.40  
  Purchase #4 $169.94   8.352%   $184.1334   $184.13   $184.15   $184.10  
  Purchase #5 $135.42   5.811%   $143.2893   $143.29   $143.30   $143.30  
  Purchase #6 $135.75   8.436%   $147.2019   $147.20   $147.20   $147.20  
  Purchase #7 $210.64   5.362%   $221.9345   $221.93   $221.95   $221.90  
  7 purchase totals = $1,057.17       $1,136.4333   $1,136.42   $1,136.45   $1,136.40