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 $214.67   11.488%   $239.3313   $239.33   $239.35   $239.30  
  Purchase #2 $43.57   7.245%   $46.7266   $46.73   $46.75   $46.70  
  Purchase #3 $196.84   9.774%   $216.0791   $216.08   $216.10   $216.10  
  Purchase #4 $107.73   11.320%   $119.925   $119.93   $119.95   $119.90  
  Purchase #5 $135.33   7.460%   $145.4256   $145.43   $145.45   $145.40  
  Purchase #6 $86.78   5.278%   $91.3602   $91.36   $91.35   $91.40  
  Purchase #7 $124.89   8.498%   $135.5032   $135.50   $135.50   $135.50  
  7 purchase totals = $909.81       $994.3510   $994.36   $994.45   $994.30