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 $154.68   7.163%   $165.7597   $165.76   $165.75   $165.80  
  Purchase #2 $239.52   3.106%   $246.9595   $246.96   $246.95   $247.00  
  Purchase #3 $192.44   7.234%   $206.3611   $206.36   $206.35   $206.40  
  Purchase #4 $220.94   3.483%   $228.6353   $228.64   $228.65   $228.60  
  Purchase #5 $93.70   4.210%   $97.6448   $97.64   $97.65   $97.60  
  Purchase #6 $48.45   13.533%   $55.0067   $55.01   $55.00   $55.00  
  Purchase #7 $166.66   10.192%   $183.646   $183.65   $183.65   $183.60  
  7 purchase totals = $1,116.39       $1,184.0131   $1,184.02   $1,184.00   $1,184.00