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 $10.65   8.109%   $11.5136   $11.51   $11.50   $11.50  
  Purchase #2 $175.57   6.341%   $186.7029   $186.70   $186.70   $186.70  
  Purchase #3 $38.49   12.308%   $43.2273   $43.23   $43.25   $43.20  
  Purchase #4 $166.34   6.819%   $177.6827   $177.68   $177.70   $177.70  
  Purchase #5 $215.32   5.405%   $226.958   $226.96   $226.95   $227.00  
  Purchase #6 $239.98   4.402%   $250.5439   $250.54   $250.55   $250.50  
  Purchase #7 $115.93   5.811%   $122.6667   $122.67   $122.65   $122.70  
  7 purchase totals = $962.28       $1,019.2951   $1,019.29   $1,019.30   $1,019.30