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 $188.87   13.713%   $214.7697   $214.77   $214.75   $214.80  
  Purchase #2 $152.50   7.124%   $163.3641   $163.36   $163.35   $163.40  
  Purchase #3 $241.31   13.787%   $274.5794   $274.58   $274.60   $274.60  
  Purchase #4 $117.92   7.603%   $126.8855   $126.89   $126.90   $126.90  
  Purchase #5 $151.52   4.771%   $158.749   $158.75   $158.75   $158.70  
  Purchase #6 $238.92   11.366%   $266.0756   $266.08   $266.10   $266.10  
  Purchase #7 $67.84   3.176%   $69.9946   $69.99   $70.00   $70.00  
  7 purchase totals = $1,158.88       $1,274.4179   $1,274.42   $1,274.45   $1,274.50