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 $103.83   6.670%   $110.7555   $110.76   $110.75   $110.80  
  Purchase #2 $130.42   4.338%   $136.0776   $136.08   $136.10   $136.10  
  Purchase #3 $214.75   3.502%   $222.2705   $222.27   $222.25   $222.30  
  Purchase #4 $232.36   8.250%   $251.5297   $251.53   $251.55   $251.50  
  Purchase #5 $225.94   4.178%   $235.3798   $235.38   $235.40   $235.40  
  Purchase #6 $46.80   3.680%   $48.5222   $48.52   $48.50   $48.50  
  Purchase #7 $23.41   6.613%   $24.9581   $24.96   $24.95   $25.00  
  7 purchase totals = $977.51       $1,029.4934   $1,029.50   $1,029.50   $1,029.60