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 $238.75   13.727%   $271.5232   $271.52   $271.50   $271.50  
  Purchase #2 $10.77   3.482%   $11.145   $11.15   $11.15   $11.10  
  Purchase #3 $23.86   9.618%   $26.1549   $26.15   $26.15   $26.20  
  Purchase #4 $205.86   6.274%   $218.7757   $218.78   $218.80   $218.80  
  Purchase #5 $84.35   4.142%   $87.8438   $87.84   $87.85   $87.80  
  Purchase #6 $215.76   3.831%   $224.0258   $224.03   $224.05   $224.00  
  Purchase #7 $60.36   9.836%   $66.297   $66.30   $66.30   $66.30  
  7 purchase totals = $839.71       $905.7654   $905.77   $905.80   $905.70