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 $116.33   6.355%   $123.7228   $123.72   $123.70   $123.70  
  Purchase #2 $120.80   7.217%   $129.5181   $129.52   $129.50   $129.50  
  Purchase #3 $213.45   6.269%   $226.8312   $226.83   $226.85   $226.80  
  Purchase #4 $46.72   6.753%   $49.875   $49.88   $49.90   $49.90  
  Purchase #5 $213.82   5.118%   $224.7633   $224.76   $224.75   $224.80  
  Purchase #6 $194.40   9.699%   $213.2549   $213.25   $213.25   $213.30  
  Purchase #7 $242.54   8.715%   $263.6774   $263.68   $263.70   $263.70  
  7 purchase totals = $1,148.06       $1,231.6427   $1,231.64   $1,231.65   $1,231.70