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 $154.52   8.738%   $168.022   $168.02   $168.00   $168.00  
  Purchase #2 $231.55   8.239%   $250.6274   $250.63   $250.65   $250.60  
  Purchase #3 $82.73   3.530%   $85.6504   $85.65   $85.65   $85.70  
  Purchase #4 $206.59   13.252%   $233.9673   $233.97   $233.95   $234.00  
  Purchase #5 $189.93   5.724%   $200.8016   $200.80   $200.80   $200.80  
  Purchase #6 $244.51   4.682%   $255.958   $255.96   $255.95   $256.00  
  Purchase #7 $11.36   12.531%   $12.7835   $12.78   $12.80   $12.80  
  7 purchase totals = $1,121.19       $1,207.8102   $1,207.81   $1,207.80   $1,207.90