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 $205.63   10.702%   $227.6365   $227.64   $227.65   $227.60  
  Purchase #2 $159.31   3.170%   $164.3601   $164.36   $164.35   $164.40  
  Purchase #3 $153.37   6.242%   $162.9434   $162.94   $162.95   $162.90  
  Purchase #4 $125.52   4.716%   $131.4395   $131.44   $131.45   $131.40  
  Purchase #5 $90.93   8.403%   $98.5708   $98.57   $98.55   $98.60  
  Purchase #6 $205.65   3.421%   $212.6853   $212.69   $212.70   $212.70  
  Purchase #7 $215.78   10.104%   $237.5824   $237.58   $237.60   $237.60  
  7 purchase totals = $1,156.19       $1,235.2180   $1,235.22   $1,235.25   $1,235.20