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 $228.34   3.452%   $236.2223   $236.22   $236.20   $236.20  
  Purchase #2 $189.72   5.221%   $199.6253   $199.63   $199.65   $199.60  
  Purchase #3 $145.92   11.124%   $162.1521   $162.15   $162.15   $162.20  
  Purchase #4 $69.46   11.446%   $77.4104   $77.41   $77.40   $77.40  
  Purchase #5 $40.87   6.716%   $43.6148   $43.61   $43.60   $43.60  
  Purchase #6 $159.88   12.334%   $179.5996   $179.60   $179.60   $179.60  
  Purchase #7 $201.60   12.164%   $226.1226   $226.12   $226.10   $226.10  
  7 purchase totals = $1,035.79       $1,124.7471   $1,124.74   $1,124.70   $1,124.70