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 $56.99   6.416%   $60.6465   $60.65   $60.65   $60.60  
  Purchase #2 $23.34   5.722%   $24.6755   $24.68   $24.70   $24.70  
  Purchase #3 $145.28   6.603%   $154.8728   $154.87   $154.85   $154.90  
  Purchase #4 $164.52   13.533%   $186.7845   $186.78   $186.80   $186.80  
  Purchase #5 $60.46   8.756%   $65.7539   $65.75   $65.75   $65.80  
  Purchase #6 $170.59   12.361%   $191.6766   $191.68   $191.70   $191.70  
  Purchase #7 $215.44   12.816%   $243.0508   $243.05   $243.05   $243.10  
  7 purchase totals = $836.62       $927.4606   $927.46   $927.50   $927.60