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 $92.35   4.814%   $96.7957   $96.80   $96.80   $96.80  
  Purchase #2 $26.35   12.416%   $29.6216   $29.62   $29.60   $29.60  
  Purchase #3 $147.32   4.689%   $154.2278   $154.23   $154.25   $154.20  
  Purchase #4 $10.96   6.219%   $11.6416   $11.64   $11.65   $11.60  
  Purchase #5 $160.32   9.841%   $176.0971   $176.10   $176.10   $176.10  
  Purchase #6 $151.76   8.373%   $164.4669   $164.47   $164.45   $164.50  
  Purchase #7 $213.46   3.358%   $220.628   $220.63   $220.65   $220.60  
  7 purchase totals = $802.52       $853.4787   $853.49   $853.50   $853.40