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 $119.47   3.390%   $123.52   $123.52   $123.50   $123.50  
  Purchase #2 $245.45   3.426%   $253.8591   $253.86   $253.85   $253.90  
  Purchase #3 $63.98   12.259%   $71.8233   $71.82   $71.80   $71.80  
  Purchase #4 $57.91   9.235%   $63.258   $63.26   $63.25   $63.30  
  Purchase #5 $138.65   9.505%   $151.8287   $151.83   $151.85   $151.80  
  Purchase #6 $77.80   8.518%   $84.427   $84.43   $84.45   $84.40  
  Purchase #7 $111.75   3.189%   $115.3137   $115.31   $115.30   $115.30  
  7 purchase totals = $815.01       $864.0298   $864.03   $864.00   $864.00