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 $24.44   6.839%   $26.1115   $26.11   $26.10   $26.10  
  Purchase #2 $82.79   9.809%   $90.9109   $90.91   $90.90   $90.90  
  Purchase #3 $147.59   13.142%   $166.9863   $166.99   $167.00   $167.00  
  Purchase #4 $37.95   8.246%   $41.0794   $41.08   $41.10   $41.10  
  Purchase #5 $11.35   11.322%   $12.635   $12.64   $12.65   $12.60  
  Purchase #6 $212.61   5.610%   $224.5374   $224.54   $224.55   $224.50  
  Purchase #7 $197.86   8.250%   $214.1835   $214.18   $214.20   $214.20  
  7 purchase totals = $714.59       $776.4440   $776.45   $776.50   $776.40