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 $106.52   12.133%   $119.4441   $119.44   $119.45   $119.40  
  Purchase #2 $224.95   9.749%   $246.8804   $246.88   $246.90   $246.90  
  Purchase #3 $159.35   10.405%   $175.9304   $175.93   $175.95   $175.90  
  Purchase #4 $13.52   4.119%   $14.0769   $14.08   $14.10   $14.10  
  Purchase #5 $91.67   4.327%   $95.6366   $95.64   $95.65   $95.60  
  Purchase #6 $136.66   7.812%   $147.3359   $147.34   $147.35   $147.30  
  Purchase #7 $113.93   11.739%   $127.3042   $127.30   $127.30   $127.30  
  7 purchase totals = $846.60       $926.6085   $926.61   $926.70   $926.50