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 $68.69   12.376%   $77.1911   $77.19   $77.20   $77.20  
  Purchase #2 $99.76   13.801%   $113.5279   $113.53   $113.55   $113.50  
  Purchase #3 $129.92   7.769%   $140.0135   $140.01   $140.00   $140.00  
  Purchase #4 $206.62   8.795%   $224.7922   $224.79   $224.80   $224.80  
  Purchase #5 $175.77   5.663%   $185.7239   $185.72   $185.70   $185.70  
  Purchase #6 $160.88   13.303%   $182.2819   $182.28   $182.30   $182.30  
  Purchase #7 $246.77   9.244%   $269.5814   $269.58   $269.60   $269.60  
  7 purchase totals = $1,088.41       $1,193.1119   $1,193.10   $1,193.15   $1,193.10