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 $69.34   10.110%   $76.3503   $76.35   $76.35   $76.40  
  Purchase #2 $10.83   9.162%   $11.8222   $11.82   $11.80   $11.80  
  Purchase #3 $34.91   4.600%   $36.5159   $36.52   $36.50   $36.50  
  Purchase #4 $56.94   3.833%   $59.1225   $59.12   $59.10   $59.10  
  Purchase #5 $216.91   9.332%   $237.152   $237.15   $237.15   $237.20  
  Purchase #6 $23.94   9.573%   $26.2318   $26.23   $26.25   $26.20  
  Purchase #7 $49.84   5.324%   $52.4935   $52.49   $52.50   $52.50  
  7 purchase totals = $462.71       $499.6882   $499.68   $499.65   $499.70