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 $111.43   4.673%   $116.6371   $116.64   $116.65   $116.60  
  Purchase #2 $170.62   7.673%   $183.7117   $183.71   $183.70   $183.70  
  Purchase #3 $207.39   9.258%   $226.5902   $226.59   $226.60   $226.60  
  Purchase #4 $49.32   12.585%   $55.5269   $55.53   $55.55   $55.50  
  Purchase #5 $30.52   9.629%   $33.4588   $33.46   $33.45   $33.50  
  Purchase #6 $96.72   3.627%   $100.228   $100.23   $100.25   $100.20  
  Purchase #7 $240.74   7.611%   $259.0627   $259.06   $259.05   $259.10  
  7 purchase totals = $906.74       $975.2154   $975.22   $975.25   $975.20