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 $192.85   11.517%   $215.0605   $215.06   $215.05   $215.10  
  Purchase #2 $86.39   13.359%   $97.9308   $97.93   $97.95   $97.90  
  Purchase #3 $212.86   5.418%   $224.3928   $224.39   $224.40   $224.40  
  Purchase #4 $249.55   5.700%   $263.7744   $263.77   $263.75   $263.80  
  Purchase #5 $208.31   8.400%   $225.808   $225.81   $225.80   $225.80  
  Purchase #6 $44.80   5.583%   $47.3012   $47.30   $47.30   $47.30  
  Purchase #7 $196.60   3.591%   $203.6599   $203.66   $203.65   $203.70  
  7 purchase totals = $1,191.36       $1,277.9276   $1,277.92   $1,277.90   $1,278.00