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 $146.53   5.636%   $154.7884   $154.79   $154.80   $154.80  
  Purchase #2 $207.94   8.519%   $225.6544   $225.65   $225.65   $225.70  
  Purchase #3 $75.76   8.786%   $82.4163   $82.42   $82.40   $82.40  
  Purchase #4 $226.51   13.840%   $257.859   $257.86   $257.85   $257.90  
  Purchase #5 $224.89   3.197%   $232.0797   $232.08   $232.10   $232.10  
  Purchase #6 $237.64   13.456%   $269.6168   $269.62   $269.60   $269.60  
  Purchase #7 $21.33   13.601%   $24.2311   $24.23   $24.25   $24.20  
  7 purchase totals = $1,140.60       $1,246.6457   $1,246.65   $1,246.65   $1,246.70