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 $204.87   10.766%   $226.9263   $226.93   $226.95   $226.90  
  Purchase #2 $63.84   4.701%   $66.8411   $66.84   $66.85   $66.80  
  Purchase #3 $121.56   11.308%   $135.306   $135.31   $135.30   $135.30  
  Purchase #4 $134.81   3.173%   $139.0875   $139.09   $139.10   $139.10  
  Purchase #5 $168.76   7.118%   $180.7723   $180.77   $180.75   $180.80  
  Purchase #6 $52.64   11.368%   $58.6241   $58.62   $58.60   $58.60  
  Purchase #7 $177.51   12.206%   $199.1769   $199.18   $199.20   $199.20  
  7 purchase totals = $923.99       $1,006.7342   $1,006.74   $1,006.75   $1,006.70