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 $94.38   7.664%   $101.6133   $101.61   $101.60   $101.60  
  Purchase #2 $232.59   13.489%   $263.9641   $263.96   $263.95   $264.00  
  Purchase #3 $200.87   13.691%   $228.3711   $228.37   $228.35   $228.40  
  Purchase #4 $43.65   7.671%   $46.9984   $47.00   $47.00   $47.00  
  Purchase #5 $228.44   13.282%   $258.7814   $258.78   $258.80   $258.80  
  Purchase #6 $163.53   10.386%   $180.5142   $180.51   $180.50   $180.50  
  Purchase #7 $122.35   12.375%   $137.4908   $137.49   $137.50   $137.50  
  7 purchase totals = $1,085.81       $1,217.7333   $1,217.72   $1,217.70   $1,217.80