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 $192.42   11.598%   $214.7369   $214.74   $214.75   $214.70  
  Purchase #2 $178.46   13.732%   $202.9661   $202.97   $202.95   $203.00  
  Purchase #3 $147.36   6.298%   $156.6407   $156.64   $156.65   $156.60  
  Purchase #4 $168.39   9.241%   $183.9509   $183.95   $183.95   $184.00  
  Purchase #5 $57.38   11.213%   $63.814   $63.81   $63.80   $63.80  
  Purchase #6 $180.31   10.397%   $199.0568   $199.06   $199.05   $199.10  
  Purchase #7 $155.93   11.115%   $173.2616   $173.26   $173.25   $173.30  
  7 purchase totals = $1,080.25       $1,194.4270   $1,194.43   $1,194.40   $1,194.50