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 $235.86   5.417%   $248.6365   $248.64   $248.65   $248.60  
  Purchase #2 $27.59   7.365%   $29.622   $29.62   $29.60   $29.60  
  Purchase #3 $238.37   6.549%   $253.9809   $253.98   $254.00   $254.00  
  Purchase #4 $178.65   13.498%   $202.7642   $202.76   $202.75   $202.80  
  Purchase #5 $113.70   10.241%   $125.344   $125.34   $125.35   $125.30  
  Purchase #6 $169.36   10.832%   $187.7051   $187.71   $187.70   $187.70  
  Purchase #7 $61.92   9.461%   $67.7783   $67.78   $67.80   $67.80  
  7 purchase totals = $1,025.45       $1,115.8310   $1,115.83   $1,115.85   $1,115.80