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 $188.45   9.186%   $205.761   $205.76   $205.75   $205.80  
  Purchase #2 $59.76   13.308%   $67.7129   $67.71   $67.70   $67.70  
  Purchase #3 $46.58   7.239%   $49.9519   $49.95   $49.95   $50.00  
  Purchase #4 $156.52   9.255%   $171.0059   $171.01   $171.00   $171.00  
  Purchase #5 $146.36   9.594%   $160.4018   $160.40   $160.40   $160.40  
  Purchase #6 $122.40   7.309%   $131.3462   $131.35   $131.35   $131.30  
  Purchase #7 $77.93   7.249%   $83.5791   $83.58   $83.60   $83.60  
  7 purchase totals = $798.00       $869.7588   $869.76   $869.75   $869.80