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 $244.30   11.659%   $272.7829   $272.78   $272.80   $272.80  
  Purchase #2 $181.65   11.689%   $202.8831   $202.88   $202.90   $202.90  
  Purchase #3 $30.73   3.305%   $31.7456   $31.75   $31.75   $31.70  
  Purchase #4 $114.88   10.509%   $126.9527   $126.95   $126.95   $127.00  
  Purchase #5 $121.74   10.183%   $134.1368   $134.14   $134.15   $134.10  
  Purchase #6 $106.91   11.796%   $119.5211   $119.52   $119.50   $119.50  
  Purchase #7 $147.66   6.873%   $157.8087   $157.81   $157.80   $157.80  
  7 purchase totals = $947.87       $1,045.8309   $1,045.83   $1,045.85   $1,045.80