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 $151.83   8.645%   $164.9557   $164.96   $164.95   $165.00  
  Purchase #2 $122.46   10.708%   $135.573   $135.57   $135.55   $135.60  
  Purchase #3 $9.32   4.411%   $9.7311   $9.73   $9.75   $9.70  
  Purchase #4 $56.75   4.599%   $59.3599   $59.36   $59.35   $59.40  
  Purchase #5 $59.43   9.414%   $65.0247   $65.02   $65.00   $65.00  
  Purchase #6 $246.82   10.220%   $272.045   $272.05   $272.05   $272.00  
  Purchase #7 $200.54   13.249%   $227.1095   $227.11   $227.10   $227.10  
  7 purchase totals = $847.15       $933.7989   $933.80   $933.75   $933.80