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 $236.45   9.581%   $259.1043   $259.10   $259.10   $259.10  
  Purchase #2 $211.81   9.781%   $232.5271   $232.53   $232.55   $232.50  
  Purchase #3 $124.60   10.781%   $138.0331   $138.03   $138.05   $138.00  
  Purchase #4 $105.35   7.511%   $113.2628   $113.26   $113.25   $113.30  
  Purchase #5 $185.85   4.772%   $194.7188   $194.72   $194.70   $194.70  
  Purchase #6 $204.77   6.655%   $218.3974   $218.40   $218.40   $218.40  
  Purchase #7 $44.83   13.203%   $50.7489   $50.75   $50.75   $50.70  
  7 purchase totals = $1,113.66       $1,206.7924   $1,206.79   $1,206.80   $1,206.70