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 $157.27   13.301%   $178.1885   $178.19   $178.20   $178.20  
  Purchase #2 $197.96   9.585%   $216.9345   $216.93   $216.95   $216.90  
  Purchase #3 $237.27   3.803%   $246.2934   $246.29   $246.30   $246.30  
  Purchase #4 $26.41   12.411%   $29.6877   $29.69   $29.70   $29.70  
  Purchase #5 $89.30   6.421%   $95.034   $95.03   $95.05   $95.00  
  Purchase #6 $223.36   11.267%   $248.526   $248.53   $248.55   $248.50  
  Purchase #7 $52.46   4.800%   $54.9781   $54.98   $55.00   $55.00  
  7 purchase totals = $984.03       $1,069.6422   $1,069.64   $1,069.75   $1,069.60