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 $61.83   5.732%   $65.3741   $65.37   $65.35   $65.40  
  Purchase #2 $180.46   4.229%   $188.0917   $188.09   $188.10   $188.10  
  Purchase #3 $52.66   8.166%   $56.9602   $56.96   $56.95   $57.00  
  Purchase #4 $233.70   8.773%   $254.2025   $254.20   $254.20   $254.20  
  Purchase #5 $232.92   10.515%   $257.4115   $257.41   $257.40   $257.40  
  Purchase #6 $230.35   8.873%   $250.789   $250.79   $250.80   $250.80  
  Purchase #7 $166.82   11.720%   $186.3713   $186.37   $186.35   $186.40  
  7 purchase totals = $1,158.74       $1,259.2003   $1,259.19   $1,259.15   $1,259.30