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 $47.37   8.866%   $51.5698   $51.57   $51.55   $51.60  
  Purchase #2 $242.25   13.746%   $275.5497   $275.55   $275.55   $275.50  
  Purchase #3 $62.93   13.849%   $71.6452   $71.65   $71.65   $71.60  
  Purchase #4 $124.82   11.645%   $139.3553   $139.36   $139.35   $139.40  
  Purchase #5 $211.93   7.773%   $228.4033   $228.40   $228.40   $228.40  
  Purchase #6 $109.97   4.651%   $115.0847   $115.08   $115.10   $115.10  
  Purchase #7 $39.65   6.687%   $42.3014   $42.30   $42.30   $42.30  
  7 purchase totals = $838.92       $923.9094   $923.91   $923.90   $923.90