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 $15.61   8.628%   $16.9568   $16.96   $16.95   $17.00  
  Purchase #2 $211.92   7.108%   $226.9833   $226.98   $227.00   $227.00  
  Purchase #3 $111.39   3.455%   $115.2385   $115.24   $115.25   $115.20  
  Purchase #4 $177.31   10.663%   $196.2166   $196.22   $196.20   $196.20  
  Purchase #5 $103.82   7.693%   $111.8069   $111.81   $111.80   $111.80  
  Purchase #6 $207.80   7.141%   $222.639   $222.64   $222.65   $222.60  
  Purchase #7 $237.83   6.177%   $252.5208   $252.52   $252.50   $252.50  
  7 purchase totals = $1,065.68       $1,142.3619   $1,142.37   $1,142.35   $1,142.30