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 $169.61   13.222%   $192.0358   $192.04   $192.05   $192.00  
  Purchase #2 $116.88   7.270%   $125.3772   $125.38   $125.40   $125.40  
  Purchase #3 $233.55   7.314%   $250.6318   $250.63   $250.65   $250.60  
  Purchase #4 $227.55   4.389%   $237.5372   $237.54   $237.55   $237.50  
  Purchase #5 $49.81   6.393%   $52.9944   $52.99   $53.00   $53.00  
  Purchase #6 $232.42   4.676%   $243.288   $243.29   $243.30   $243.30  
  Purchase #7 $236.86   13.132%   $267.9645   $267.96   $267.95   $268.00  
  7 purchase totals = $1,266.68       $1,369.8289   $1,369.83   $1,369.90   $1,369.80