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 $213.48   13.252%   $241.7704   $241.77   $241.75   $241.80  
  Purchase #2 $152.61   4.403%   $159.3294   $159.33   $159.35   $159.30  
  Purchase #3 $114.66   7.570%   $123.3398   $123.34   $123.35   $123.30  
  Purchase #4 $60.27   3.822%   $62.5735   $62.57   $62.55   $62.60  
  Purchase #5 $177.30   8.456%   $192.2925   $192.29   $192.30   $192.30  
  Purchase #6 $243.97   4.273%   $254.3948   $254.39   $254.40   $254.40  
  Purchase #7 $97.76   5.528%   $103.1642   $103.16   $103.15   $103.20  
  7 purchase totals = $1,060.05       $1,136.8646   $1,136.85   $1,136.85   $1,136.90