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 $60.66   3.871%   $63.0081   $63.01   $63.00   $63.00  
  Purchase #2 $164.89   8.374%   $178.6979   $178.70   $178.70   $178.70  
  Purchase #3 $41.66   7.818%   $44.917   $44.92   $44.90   $44.90  
  Purchase #4 $210.72   5.563%   $222.4424   $222.44   $222.45   $222.40  
  Purchase #5 $160.60   8.655%   $174.4999   $174.50   $174.50   $174.50  
  Purchase #6 $106.90   11.133%   $118.8012   $118.80   $118.80   $118.80  
  Purchase #7 $54.42   5.174%   $57.2357   $57.24   $57.25   $57.20  
  7 purchase totals = $799.85       $859.6022   $859.61   $859.60   $859.50