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 $59.70   5.773%   $63.1465   $63.15   $63.15   $63.10  
  Purchase #2 $54.80   5.405%   $57.7619   $57.76   $57.75   $57.80  
  Purchase #3 $188.83   6.321%   $200.7659   $200.77   $200.75   $200.80  
  Purchase #4 $191.47   5.384%   $201.7787   $201.78   $201.80   $201.80  
  Purchase #5 $57.25   4.717%   $59.9505   $59.95   $59.95   $60.00  
  Purchase #6 $77.51   5.658%   $81.8955   $81.90   $81.90   $81.90  
  Purchase #7 $219.48   12.668%   $247.2837   $247.28   $247.30   $247.30  
  7 purchase totals = $849.04       $912.5827   $912.59   $912.60   $912.70